User terminal, radio base station and radio communication method

ABSTRACT

The present invention is designed to suitably realize UCI (Uplink Control Information) transmission at a desired timing in a carrier where LBT (Listen Before Talk) is configured. A user terminal, according to one embodiment of the present invention, has a transmission section that transmits signals in carriers where listening is performed before uplink transmission, a receiving section that receives PUCCH cell configuration information as to whether or not at least one of the carriers is a cell where a PUCCH (Physical Uplink Control Channel) is transmitted, and a control section that controls the transmission of uplink control information (UCI) in the carriers based on the PUCCH cell configuration information.

TECHNICAL FIELD

The present invention relates to a user terminal, a radio base stationand a radio communication method in a next-generation mobilecommunication system.

BACKGROUND ART

In the UMTS Universal Mobile Telecommunications System) network, thespecifications of long-term evolution (LTE) have been drafted for thepurpose of further increasing high speed data rates, providing lowerdelays and so on (see non-patent literature 1). Also, the specificationsof LTE-A (also referred to as LTE-advanced, LTE Rel. 10, 11 or 12, etc.)have been drafted for further broadbandization and increased speedbeyond LTE (also referred to as LTE Rel. 8 or 9), and successor systemsof LTE (also referred to as, for example, FRA (Future Radio Access), 5G(5th generation mobile communication system), LTE Rel. 13 and so on) areunder study.

The specifications of Rel. 8 to 12 LTE have been drafted assumingexclusive operation in frequency bands that are licensed to operators(also referred to as “licensed bands”). As licensed bands, for example,800 MHz, 1.7 GHz and 2 GHz are used.

In recent years, user traffic has been increasing steeply following thespread of high-performance user terminals (UE: User Equipment) such assmart-phones and tablets. Although more frequency bands need to be addedto accommodate this increasing user traffic, licensed bands have limitedspectra (licensed spectra).

Consequently, a study is in progress with Rel. 13 LTE to enhance thefrequencies of LTE systems by using bands of unlicensed spectra (alsoreferred to as “unlicensed bands”) that are available for use apart fromlicensed bands (see non-patent literature 2). For example, the 2.4 GHzband and the 5 GHz band, where Wi-Fi (registered trademark) andBluetooth (registered trademark) can be used, are under study for use asunlicensed bands.

To be more specific, with Rel. 13 LTE, a study is in progress to executecarrier aggregation (CA) between licensed bands and unlicensed bands.Communication that is carried out by using unlicensed bands withlicensed bands like this is referred to as “LAA” (License-AssistedAccess). Note that, in the future, dual connectivity (DC) betweenlicensed bands and unlicensed bands and stand-alone (SA) of unlicensedbands may become the subject of study under LAA.

For unlicensed bands in which LAA is run, a study is in progress tointroduce interference control functionality in order to allowco-presence with other operators' LTE, Wi-Fi or different systems. InWi-Fi, LBT (Listen Before Talk), which is based on CCA (Clear ChannelAssessment), is used as an interference control function for use withinthe same frequency. LBT refers to the technique of “listening” (sensing)before transmitting signals, and controlling transmission based on theresult of listening. For example, in Japan and Europe, the LBT functionis stipulated as mandatory in systems that run in the 5 GHz unlicensedband such as Wi-Fi.

CITATION LIST Non-Patent Literature

-   Non-Patent Literature 1: 3GPP TS36.300 V8.12.0 “Evolved Universal    Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial    Radio Access Network (E-UTRAN); Overall description; Stage 2    (Release 8),” April 2010-   Non-Patent Literature 2: AT&T, “Drivers, Benefits and Challenges for    LTE in Unlicensed Spectrum, 3GPP TSG-RAN Meeting #62 RP-131701,”    Nov. 26, 2013

SUMMARY OF THE INVENTION Technical Problem

Now, research is on-going to transmit uplink control information (UCI)in cells of unlicensed bands. However, in cells of unlicensed bands,whether or not transmission is possible changes depending on the resultof LBT, and, unless the UCI transmission operation in unlicensed bandcells is adequately specified, UCI may not be transmitted at desiredtiming, and the throughput of communication and/or the quality ofcommunication may be degraded.

The present invention has been made in view of the above, and it istherefore an object of the present invention to provide a user terminal,a radio base station and a radio communication method, whereby UCI canbe transmitted adequately, at desired timing, in a carrier where LBT isconfigured.

Solution to Problem

According to one aspect of the present invention, a user terminal has atransmission section that transmits signals in carriers where listeningis performed before uplink transmission, a receiving section thatreceives PUCCH cell configuration information as to whether or not atleast one of the carriers is a cell where a PUCCH (Physical UplinkControl Channel) is transmitted, and a control section that controlstransmission of uplink control information (UCI) in the carriers basedon the PUCCH cell configuration information.

Technical Advantage of the Invention

According to the present invention, it is possible to transmit UCIadequately, at a desired timing in a carrier where LBT is configured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram to explain the UCI transmission operation accordingto embodiment 2.1;

FIG. 2 is a diagram to explain the UCI transmission operation accordingto embodiment 2.2;

FIG. 3 is a diagram to illustrate an example of the UCI retentionoperation according to an alternative example of a second embodiment;

FIG. 4 is a diagram to illustrate examples of UCI transmission modesaccording to a third embodiment;

FIGS. 5A and 5B are diagrams to illustrate examples of transmissioncontrol in UCI transmission mode 1;

FIGS. 6A and 6B are diagrams to illustrate examples of transmissioncontrol in UCI transmission mode 2;

FIGS. 7A and 7B are diagrams to illustrate examples of transmissioncontrol in UCI transmission mode 3;

FIG. 8 is a diagram to illustrate an example of the UCI retentionoperation in UCI transmission mode 3 according to the third embodiment;

FIG. 9 is a diagram to illustrate another example of the UCI retentionoperation in UCI transmission mode 3 according to the third embodiment;

FIG. 10 is a diagram to illustrate yet another example of the UCIretention operation in UCI transmission mode 3 according to the thirdembodiment;

FIG. 11 is a diagram to illustrate an example of a schematic structureof a radio communication system according to one embodiment of thepresent invention;

FIG. 12 is a diagram to illustrate an example of an overall structure ofa radio base station according to one embodiment of the presentinvention;

FIG. 13 is a diagram to illustrate an example of a functional structureof a radio base station according to one embodiment of the presentinvention;

FIG. 14 is a diagram to illustrate an example of an overall structure ofa user terminal according to one embodiment of the present invention;

FIG. 15 is a diagram to illustrate an example of a functional structureof a user terminal according to one embodiment of the present invention;

FIG. 16 is a diagram to illustrate an example hardware structure of aradio base station and a user terminal according to one embodiment ofthe present invention;

FIG. 17 is a diagram to illustrate an example of the method ofdetermining the codebook size according to a fourth embodiment;

FIG. 18 is a diagram to illustrate another example of the method ofdetermining the codebook size according to the fourth embodiment; and

FIG. 19 is a diagram to illustrate another example of the method ofdetermining the codebook size according to the fourth embodiment.

DESCRIPTION OF EMBODIMENTS

In systems that run LTE/LTE-A in unlicensed bands (for example, LAAsystems), interference control functionality is likely to be necessaryin order to allow co-presence with other operators' LTE, Wi-Fi and/orother systems. Note that systems that run LTE/LTE-A in unlicensed bandsmay be collectively referred to as “LAA,” “LAA-LTE,” “LTE-U,” “U-LTE”and so on, regardless of whether the mode of operation is CA, DC or SA.

Generally speaking, when a transmission point (for example, a radio basestation (eNB), a user terminal (UE) and so on) that communicates byusing a carrier of an unlicensed band (which may also be referred to asan “unlicensed cell,” an “unlicensed CC,” etc.) detects another entity(for example, another UE) that is communicating in this unlicensed bandcarrier, the transmission point is disallowed to make transmission inthis carrier.

In this case, the transmission point executes listening (LBT) at atiming that is a predetermined period ahead of transmission timing. Tobe more specific, by executing LBT, the transmission point searches thewhole applicable carrier band (for example, one component carrier (CC))at a timing that is a predetermined period ahead of a transmissiontiming, and checks whether or not other devices (for example, radio basestations, UEs, Wi-Fi devices and so on) are communicating in thiscarrier band.

Note that, in the present specification, “listening” refers to theoperation which a given transmission point (for example, a radio basestation, a user terminal, etc.) performs before transmitting signals, inorder to check whether or not signals to exceed a predetermined level(for example, predetermined power) are being transmitted from othertransmission points. Also, this “listening” performed by radio basestations and/or user terminals may be referred to as “LBT,” “CCA,”“carrier sensing” and so on.

Also, for example, LBT that is performed by an eNB prior to downlinktransmission may be referred to as “DL LBT,” and, for example, LBT thatis performed by a UE prior to uplink transmission may be referred to as“UL-LBT.” Information about the carrier where UL-LBT is to be carriedout may be reported to the UE, and, based on this information, the UEmay identify the carrier and execute UL-LBT.

The transmission point then carries out transmission using this carrieronly if it is confirmed that no other apparatus is communicating. Forexample, if the received power measured by LBT (the received signalpower during the LBT period) is equal to or lower than a predeterminedthreshold, the transmission point determines that the channel is in freestate (LBT free) free and carries out transmission. When a “channel isin free state,” this means that, in other words, the channel is notoccupied by a specific system, and it is equally possible to say that achannel is “idle,” a channel is “clear,” a channel is “free,” and so on.

On the other hand, if only just a portion of the target carrier band isdetected to be used by another piece of apparatus, the transmissionpoint stops its transmission. For example, if the transmission pointdetects that the received power of a signal from another piece ofapparatus in this band exceeds a predetermined threshold, thetransmission point determines the channel is in the busy state(LBT_(busy)), and makes no transmission. In the event LBT_(busy) isyielded, LBT is carried out again with respect to this channel, and thechannel becomes available for use only after the free state isconfirmed. Note that the method of judging whether a channel is in thefree state or in the busy state based on LBT is by no means limited tothis.

As LBT mechanisms (schemes), FBE (Frame Based Equipment) and LBE (LoadBased Equipment) are currently under study. Differences between theseinclude the frame configurations to use for transmission/receipt, thechannel-occupying time, and so on. In FBE, the LBT-relatedtransmitting/receiving configurations have fixed timings. Also, in LBE,the LBT-related transmitting/receiving configurations are not fixed inthe time direction, and LBT is carried out on an as-needed basis.

To be more specific, FBE has a fixed frame cycle, and is a mechanism ofcarrying out transmission if the result of executing carrier sensing fora certain period (which may be referred to as “LBT duration” and so on)in a predetermined frame indicates that a channel is available for use,and not making transmission but waiting until the next carrier sensingtiming if no channel is available.

On the other hand, LBE refers to a mechanism for implementing the ECCA(Extended CCA) procedure of extending the duration of carrier sensingwhen the result of carrier sensing (initial CCA) indicates that nochannel is available for use, and continuing executing carrier sensinguntil a channel is available. In LBE, random backoff is required toadequately avoid contention.

Note that the duration of carrier sensing (also referred to as the“carrier sensing period”) refers to the time (for example, the durationof one symbol) it takes to gain one LBT result by performing listeningand/or other processes and deciding whether or not a channel can beused.

A transmission point can transmit a predetermined signal (for example, achannel reservation signal) based on the result of LBT. Here, the resultof LBT refers to information about the state of channel availability(for example, “LBT_(free),” “LBT_(busy),” etc.), which is acquired byLBT in carriers where LBT is configured.

Also, when a transmission point starts transmission based on an LBTresult that indicates the free state (LBT_(free)) the transmission pointcan skip LBT and still carry out transmission, for a predeterminedperiod (for example, for 10 to 13 ms). This transmission is alsoreferred to as “burst transmission,” “burst,” “transmission burst,” andso on.

As described above, by introducing interference control that is based onLBT mechanism and that is for use within the same frequency totransmission points in LAA systems, it becomes possible to preventinterference between LAA and Wi-Fi, interference between LAA systems andso on. Furthermore, even when transmission points are controlledindependently per operator that runs an LAA system, LBT makes itpossible to reduce interference without learning the details of eachoperator's control.

Also, in LTE/LTE-A, a user terminal (UE: User Equipment) feeds backuplink control information (UCI) to a device on the network side (whichis, for example, a radio base station (eNB: eNode B)). The UE transmitsUCI by using an uplink control channel (PUCCH: Physical Uplink ControlChannel).

Also, at times where uplink data transmission is scheduled, the UE maytransmit UCI by using an uplink shared channel (PUSCH: Physical UplinkShared Channel). The radio base station performs data retransmissioncontrol, scheduling control and so on, for the UE, based on the UCIreceived.

UCI that is stipulated in LTE includes channel state information (CSI),which is comprised of a channel quality indicator (CQI), a precodingmatrix indicator (PMI), a rank indicator (RI) and so on, retransmissioncontrol information (also referred to as “HARQ-ACK (Hybrid AutomaticRepeat reQuest-ACKnowledgment),” “ACK/NACK,” “A/N,” etc.), a schedulingrequest (SR), and so on.

LAA systems are assumed to apply carrier aggregation to cells oflicensed bands (also referred to as “licensed carriers,” “licensed CCs,”etc.) and cells of unlicensed bands (also referred to as “unlicensedcarriers,” “unlicensed CCs,” etc.). Assuming this case, a study is inprogress to use unlicensed CCs as secondary cells (SCells). Note thatSCells that operate on unlicensed bands may be referred to as “LAASCells,” for example.

While research is in progress to transmit UCI in LAA SCells, there is anon-going discussion as to which cells' UCI is to be transmitted in LAASCells. For example, one idea under discussion is not to transmitHARQ-ACKs pertaining to licensed CCs in the UL for LAA SCells. This isbecause the throughput of licensed CCs will decrease if HARQ-ACKspertaining to licensed CCs cannot be sent due to “LBT_(busy)” and/or thelike.

Also, a study is conducted to allow HARQ-ACKs and CSIs for unlicensedCCs to be transmitted in the UL of LAA SCells. This is to prevent theprimary cell (PCell) of licensed CCs from entering the overload statewith a large amount of UCI.

It is not yet decided whether PUCCH can be used when UCI, or even a partof UCI, is transmitted in unlicensed CCs, but it is necessary to decidehow to send UCI both when PUCCH is supported and when PUCCH is notsupported. In any case, it may be possible to re-use part of existingUCI transmission control methods.

One existing UCI transmission control method is a method to use PUCCHgroups. With the PUCCH groups used in DC, eCA (enhanced CA) and so on,up to two PUCCH groups are configured in a UE. It is possible toconfigure one PUCCH cell in each group. A PUCCH cell refers to a cellthat is configured to transmit PUCCH. The UCI for CCs in a given groupcan be transmitted in the PUCCH, using the same group's PUCCH cell. Notethat the PUCCH cell is not limited to PCell.

Another existing method for controlling UCI transmission is simultaneoustransmission of PUCCH and PUSCH. For example, a UE where simultaneoustransmission of PUCCH and PUSCH (hereinafter referred to as “PUCCH+PUSCHsimultaneous transmission”) is configured (configured “true”) cantransmit HARQ-ACKs in PUCCH and CSI in PUSCH, at the same time. Notethat periodic CSI (P-CSI) may be reported in the cell with the smallestcell index (for example, an SCell index) among the cells where PUSCH isallocated, and aperiodic CSI (A-CSI) may be reported in triggered cells.

For example, if PUCCH can be used in LAA SCells, it may be possible tore-use existing concepts related to the design of PUCCH groups. In thiscase, it may be possible to configure a PUCCH group consisting only oflicensed CCs and a PUCCH group consisting only of unlicensed CCs, andtransmit the UCI for each PUCCH group in the PUCCH cells of that group.Note that PUCCH+PUSCH simultaneous transmission may be configured perPUCCH group, individually. Furthermore, the PUCCH groups may be referredto as “cell groups.”

However, in this case, in the unlicensed CCs, whether or not PUCCHand/or PUSCH can be transmitted changes depending on what result LBTindicates, and therefore how to define the UCI transmission operation inthe PUCCH group of unlicensed CCs raises a problem.

Meanwhile, if PUCCH cannot be used in LAA SCells, how to specify the UCItransmission operation in each CC, taking into account the constraintsof PUCCH+PUSCH simultaneous transmission, LBT and so on, poses aproblem. The reasons that PUCCH cannot be used in LAA SCell may include,for example, that PUCCH is not supported in the specification, thatPUCCH is not configured because PUCCH+PUSCH simultaneous transmissionleads to a power-limited state and makes it difficult to achievesufficient quality, and so on.

Also, although PUCCH+PUSCH simultaneous transmission between differentcells is already supported in licensed CCs, the operation in unlicensedCCs has not been studied.

So, the present inventors have come up with the idea of clearly definingthe UCI transmission operation (transmission control) in LAA SCells,both when PUCCH is used and when PUSCH is used.

To do so, the present inventors have first started out with the idea ofconfiguring whether or not PUCCH transmission in LAA SCells is possiblevia RRC (Radio Resource Control) signaling. In addition, assuming thecase where PUCCH transmission is configured, the present inventors havecome up with the idea of specifying separate UE operations depending onwhether or not PUCCH+PUSCH simultaneous transmission is possible. Inaddition, the present inventors have come up with the idea of definingUE operations in multiple different UCI transmission modes when PUCCHtransmission is not configured, so that eNB can configure the UCItransmission mode for the UE.

Now, embodiments of the present invention will be described in detailbelow with reference to the accompanying drawings. For each embodiment,a UE will be described to perform UL-LBT in LAA SCells, but this is notlimiting.

Also, although each embodiment will be described on the assumption thatCA is applied to PCell that is a license cell and SCell that is anunlicensed cell, but this is not limiting.

That is, in each embodiment, the structure in which licensed carriersare regarded as carriers where listening (LBT) is not configured (whichmay be referred to as “carriers where LBT is not executed,” “carrierswhere LBT cannot be executed,” “non-LBT carriers,” etc.), and thestructure in which unlicensed carriers are regarded as carriers wherelistening (LBT) is configured (which may be referred to as “carrierswhere LBT is executed”, “carriers where LBT should be executed”, “LBTcarriers,” etc.) also constitute embodiments of the present invention.

Also, the combinations of carriers where LBT is not configured andcarriers where LBT is configured, and PCell and SCells are not limitedto those given above. For example, the present invention can be appliedto the case where a UE connects with an unlicensed band in stand-alone(when PCell and SCells are all carriers where LBT is configured), and soon.

(Radio Communication Method)

First Embodiment

According to the first embodiment of the present invention, a UE reportsinformation as to whether or not the UE supports transmission in PUCCHformat (PF: PUCCH Format) 4 and/or 5 (whether or not to support PF 4/5)in LAA SCells, to the network side (for example, eNB), as terminalcapability information (UE capability).

This capability information here may be reported using one or acombination of the following: (1) Existing UE capability informationbits (capability bits) to indicate that PF 4/5 are supported (these bitsmay be included and reported in, for example, PhyLayerParameters-v13x0,which is specified as a parameter for LTE Rel. 13); (2) New UEcapability information bits to indicate that PF 4/5 are supported in LAASCells (these bits may be included, for example, inPhyLayerParameters-v14x0, which is defined as a parameter for LTE Rel.14, and reported as UL-LAA-specific information); (3) L-LAA UEcapability information, including capability information to indicatethat PF 4/5 are supported in LAA SCells (for example, included andreported in, for example, supportOfLAA-r14 specified as a parameter forLTE Rel. 14).

Note that above (3) means that a UE that supports UL-LAA always supportsPF 4/5 in LAA SCells.

Also, the eNB may configure information as to whether to use PUCCH in agiven LAA SCell—that is, information about whether or not a given LAASCell is a PUCCH cell (PUCCH cell configuration information—in the UEvia higher layer signaling (for example, RRC signaling). For example,whether or not an LAA SCell is a PUCCH cell may be included in theinformation that is used to identify the UE-specific physical channelconfiguration related to the SCell (PhysicalConfigDedicatedSCell-r10),in the form of pucch-Cell-r14, which is defined as a parameter for LTERel. 14, and reported to the UE.

The PUCCH cell configuration information can also be seen as informationto indicate whether or not a given cell is a PUCCH-transmitting cell.Note that, when at least one of the above-described types of UEcapability information is received from a predetermined UE, the eNB mayreport PUCCH cell configuration information to the UE.

According to the first embodiment described above, the eNB canpreferably controls the PUCCH configuration in LAA SCells based on UEcapability information transmitted from the UE.

Note that, although the first embodiment has been described so that,when UCI for an LAA SCell is transmitted in PUCCH, whether or not PUCCHtransmission is supported in the LAA SCell is reported by using UEcapability information that indicates whether PF 4/5 are supported inthe LAA SCell, on the assumption that only PF 4/5 are used as PUCCHformats, but this is by no means limiting.

For example, when a predetermined PF (for example, PF 2) other than PF4/5 is used in an LAA SCell, whether or not PUCCH transmission issupported in the LAA SCell may be reported by using UE capabilityinformation that indicates whether or not this predetermined PF issupported in the LAA SCell. In addition, information as to whether ornot PUCCH transmission is supported in the LAA SCell may be directlyincluded and reported in the UE capability information. In this case,when the eNB receives this information from a predetermined UE, the eNBmay perform control assuming that the UE supports PF 4/5.

Second Embodiment

In the second embodiment of the present invention, the UE operation inthe case where PUCCH transmission (PUCCH on LAA SCell) is configured inLAA SCells will be defined. Below, the second embodiment will be roughlydivided into two cases—namely, the case where PUCCH+PUSCH simultaneoustransmission is not possible (configured “false”) (embodiment 2.1) andthe case where PUCCH+PUSCH simultaneous transmission is possible(configured “true”) (embodiment 2.2)—and each case will be described.Information as to whether or not simultaneous PUCCH+PUSCH transmissionis possible can be reported (configured) to a UE through higher layersignaling (for example, RRC signaling).

In the second embodiment, as mentioned earlier, a PUCCH group consistingonly of licensed CCs and a PUCCH group consisting only of unlicensed CCsare provided, and, when the UCI for each PUCCH group is transmitted inPUCCH, it is transmitted in the PUCCH cells of that group. However, theUCI transmission control according to the second embodiment can beapplied even if another CC configuration and/or group configuration isconfigured in the UE.

In the following description, only the UCI transmission operationrelated to the PUCCH group (cell group) including unlicensed CCs will bedescribed, and the description of the PUCCH group including licensed CCswill be omitted.

Embodiment 2.1

FIG. 1 is a diagram to explain the UCI transmission operation accordingto embodiment 2.1. FIG. 1 illustrates three LAA SCells. “PUCCH SCell” isan LAA SCell that is capable of PUCCH transmission (configured as aPUCCH cell). “LAA SCell_(i)” and “LAA SCell_(i+1)” are LAA SCells thatcannot perform PUCCH transmission (not configured as PUCCH cells).Assume that the SCell index of LAA SCell_(i) is smaller than that ofeither LAA SCell_(i+1) or the PUCCH SCell. Note that application of thisembodiment is not limited to the case where a UE uses three LAA SCells.

In FIG. 1, a UE executes listening in the CCA period before transmittingUL signals in each SCell, and, upon judging that the channel is idle,the UE carries out UL transmission. In addition, periods t₁₁ to t₁₄illustrated in FIG. 1 are simply exemplary periods for explaining theUCI transmission operation, and the order these periods occur, thelength of these periods and so on are not limited.

At a timing (for example, a TTI) where PUSCH is not scheduled in eitherLAA SCell, the UCI for all of the unlicensed CCs (in the PUCCH group)(including A/N, CSI (P-CSI, A-CSI, etc.), SR and others) is transmitted(exemplified at t₁₁) in the PUCCHs of the LAA SCells based on LBT (PUCCHon LAA SCell). However, A-CSI for SCells other than the PUCCH SCell maynot be transmitted in the PUCCH SCell.

Note that, referring to FIG. 1, UCI that needs not be transmitted maynot be transmitted even if it is illustrated in the drawing. Forexample, at t₁₁, at least one of A/N, CSI (P-CSI, A-CSI, etc.) and SRmay be transmitted. The same applies to the other UCIs illustrated inthe drawing, and the same applies to the subsequent drawings.

The UE shall transmit PUCCH in PF 4/5 in the LAA SCells, but other PFsmay be used as well. Note that at a timing where only one P-CSI istransmitted in PUCCH, the UE may transmit this one P-CSI in accordancewith PF 4 and/or 5, or transmit this one P-CSI in accordance with anexisting PF (for example, PF 2).

At a timing where PUSCH is scheduled in LAA SCells and A/N and/or P-CSIis triggered (A/N and/or P-CSI is transmitted), the UE transmits A/Nand/or P-CSI based on LBT, in the PUSCH of a particular cell among theLAA SCells that are scheduled (exemplified at t₁₂). In this case, the UEtries to transmit UCI only in one of the LAA SCells that are scheduled,so that the efficiency of the use of resources can be improved by nottransmitting redundant UCIs. At t₁₂, the UE uses LAA SCell_(i) as thespecific cell.

Here, the specific cell may be, for example, the cell where apredetermined cell-related indicator is the smallest among the LAASCells that are scheduled. The predetermined indicator may be a cell ID(cell identity), a physical cell ID, a virtual cell ID, a cell index(for example, an SCell index, an index that is unique to LAA SCells,etc.), or other indicators.

Also, at a timing where PUSCH is scheduled in LAA SCells and A/N and/orP-CSI are triggered, the UE transmits A/N and/or P-CSI based on LBT inthe PUSCHs of all the scheduled LAA SCells (exemplified at t₁₃). In thiscase, the UE can try transmitting UCI of the same contents in all of theLAA SCells that are scheduled, so that the possibility that the UE willsuccessfully transmit the UCI can be improved.

Also, at a timing where PUSCH is scheduled in a predetermined LAA SCelland A-CSI is triggered (A-CSI is transmitted) in this LAA SCell, the UEtransmits A-CSI based on LTB, in the PUSCH of this LAA SCell(exemplified at t₁₄). In this case, the A-CSI is transmitted only in theA-CSI-triggered cell, so that the communication overhead related to thereporting of A-CSI can be distributed over each cell. In addition, whenhaving A/N that should be transmitted, the UE may transmit (piggyback)the A-CSI and the A/N together.

Embodiment 2.2

FIG. 2 is a diagram to explain the UCI transmission operation accordingto embodiment 2.2. FIG. 2 illustrates a similar example to FIG. 1.

At a timing where at least one of A/N, P-CSI and SR should betransmitted (for example, TTI), the UE transmits the UCI based on theLBT in the PUCCH on the LAA SCell (PUCCH SCell) (illustrated as t₂₁,t₂₃, t₂₄ and t₂₅).

FIG. 2 illustrates an example in which the UE transmits PUCCH in PF 4/5in LAA SCells, but different PFs may be used as well. Note that at atiming where only one P-CSI is transmitted in PUCCH, the UE may transmitthis one P-CSI in PF 4 and/or 5, or transmit this one P-CSI in anexisting PF (for example, PF 2).

At a timing where A-CSI is triggered (A-CSI is transmitted), the UEtransmits A-CSI based on LBT using the PUSCH of the triggered cell(exemplified at t₂₂ and t₂₅). For example, at t₂₂, A-CSI (A-CSI_(i)) forLAA SCell_(i) is transmitted in LAA SCell_(i).

Alternative Example of Second Embodiment

When UCI is transmitted in an unlicensed CC, there is a possibility thatLBT fails (the result of LBT indicates “busy”) and a delay is producedbefore PUCCH and/or PUSCH are transmitted. When transmission of UCI isdelayed and the UCI that is already generated is immediately discarded,unnecessary UCI generation processing might take place in the UE, andthe processing load in the UE may increase.

So, the UE may retain the UCI for a predetermined period (which may bereferred to as “UCI retention period,” “PUCCH-related UCI retentionperiod,” etc.). By this means, the UE can transmit all the UCI that hasbeen retained, at the time LBT succeeds (the result of LBT indicates“free”). For example, UCI may be retained by storing UCI in apredetermined buffer area.

The UCI retention period may be defined as a period, which starts fromthe time resource of a PUCCH that may be able to transmit given UCIfirst (for example, TTI), and in which this UCI can be transmitted inthe PUCCH. Also, the UCI retention period may be defined with a fixedvalue in advance in the specification, or may be reported from the eNBby using higher layer signaling (for example, RRC signaling, broadcastinformation (MIB (Master Information Block), SIB (System InformationBlock), etc.), physical layer signaling (for example, downlink controlinformation (DCI)), or a combination of these.

Note that, once UCI is successfully transmitted, the UCI discards thisUCI even during the UCI retention period. Meanwhile, even after UCI issuccessfully transmitted, the UE may retain this UCI during the UCIretention period.

FIG. 3 is a diagram to illustrate an example of the UCI retentionoperation according to an alternative example of the second embodiment.FIG. 3 illustrates downlink signals (DL Tx) received in a UE, uplinkresources for a PUCCH SCell and UCIs (A/N) that are transmitted. FIG. 3assumes a TTI duration of 1 ms, but the TTI duration is not limited tothis.

In FIG. 3, the UE receives downlink signals (downlink data) in twelveconsecutive TTIs. an A/N (A/N_(j)) is generated in response to thereceipt of a downlink signal in the j-th TTI, and retained. In this way,every time the UE receives a downlink signal, the UE generates an A/N inresponse, and retains this. In FIG. 3, the UCI retention period (X) isconfigured to 9 ms. Consequently, each A/N_(j) is discarded after it isretained for 9 ms. That is, it is possible to say that the maximumnumber of UCIs (A/Ns) that can be retained in the buffer is the valuegiven by dividing the UCI retention period by the TTI duration.

The UE performs LBT-based UL transmission (including UCI transmission)using PUCCH, in an XSCell, a predetermined period of time (for example,4 ms) after downlink data is received. Note that, since the “UCI to betransmitted” cannot be transmitted depending on the result of LBT (forexample, in TTIs where “X” overlaps “UL” in the drawing), there arecases where “UCI scheduled to be transmitted” is indicated. According tothis example, even after UCI is successfully transmitted, the UCI isretained during the UCI retention period, and transmission continuesduring the retention period.

In this example, the UE can transmit UCI as long as the UCI retentionperiod (X) continues, and therefore the possibility that each UCI cantransmit each UCI in an LAA SCell (XSCell) can be improved.

Note that, although FIG. 3 illustrates an example in which UCI istransmitted in PUCCH, this is not limiting. For example, even when theUE transmits UCI in PUSCH, or transmits UCI in PUCCH and in PUSCH, theUE may likewise control the UCI transmission process based on the UCIretention period.

Also, the UCI retention period may be configured/specified individuallyfor each type of UCI. For example, the UCI retention period for A/Ns,the UCI retention period for P-CSI, the UCI retention period for A-CSIand the UCI retention for the SR period may be configured/defineddifferently, or may be configured/defined the same.

Third Embodiment

A third embodiment of the present invention will define the UE operationin the case where PUCCH transmission is not configured in an LAA SCell(PUCCH on LAA SCell).

In the third embodiment, a plurality of UCI transmission modes (UCI Tx(Transmission) modes) will be defined, which are used to specify whetherto transmit the UCI of each CC in a licensed carrier or an unlicensedcarrier. Then, the eNB configures (reports) based on which UCItransmission mode the UE should perform transmission control, via higherlayer signaling (for example, RRC signaling), physical layer signaling(for example, DCI), or a combination of these.

FIG. 4 is a diagram to illustrate examples of UCI transmission modesaccording to the third embodiment. UCI transmission mode 0 is a mode ofsending all the UCI related to the unlicensed CC in the licensed CC. InUCI transmission mode 1, only the A-CSI related to the unlicensed CC issent in the unlicensed CC, and the rest of the UCI is sent in thelicensed CC. In UCI transmission mode 2, CSI (P-CSI and A-CSI) relatedto the unlicensed CC is sent in the unlicensed CC, and the A/N relatedto the unlicensed CC is sent in the licensed CC. UCI transmission mode 3is a mode of sending all the UCI related to the unlicensed CC in theunlicensed CC.

Although not illustrated in FIG. 4, an SR pertaining to the unlicensedCC may be transmitted, for example, in the CC where an A/N for theunlicensed CC is transmitted, may be transmitted in the licensed CC atall times, or may be transmitted in the CC where the rest of the UCI istransmitted.

Hereinafter, points of each transmission mode according to the thirdembodiment that are of particular importance will be described indetail. Transmission control for UCI not specifically mentioned in eachtransmission mode may be the same as the transmission control in eCA ofLTE Rel. 13.

Note that FIG. 5 to FIG. 7, which will be used in the followingdescription, illustrate a PCell, which is a licensed CC, and a licensedSCell_(n), LAA SCell (and LAA SCell_(i+1)), which is an unlicensed CC,and uplink signals for each cell. LAA SCell_(i) is the cell with thesmallest SCell index among LAA SCells. Note that PCell can also bereferred to as the PUCCH cell of licensed carriers.

[UCI Transmission Mode 0]

In UCI transmission mode 0, in which in licensed CC A-CSI relating to anunlicensed CC is to be transmitted may be defined in the specificationin advance, or may be configured in the UE via RRC signaling and so on.

[UCI Transmission Mode 1]

FIG. 5 provide diagrams to illustrate examples of transmission controlaccording to UCI transmission mode 1. In UCI transmission mode 1, wherePUCCH+PUSCH simultaneous transmission is not possible, at a timing wherePUSCH is scheduled only in the unlicensed CC, the UE drops the P-CSI forthe unlicensed CC (FIG. 5A). FIG. 5A illustrates an example of droppingthe P-CSI (P-CSI_(i)) for LAA SCell_(i) at a timing where PUSCH isscheduled only in LAA SCell_(i).

Also, in UCI transmission mode 1 where PUCCH+PUSCH simultaneoustransmission is not possible, at a timing where PUSCH is scheduled onlyin the unlicensed CC and PF 3 is used in the PCell, the UE drops theP-CSI for the unlicensed CC (FIG. 5B).

Note that, in UCI transmission mode 1, as illustrated in FIG. 5, at atiming where PUSCH is scheduled in the licensed CC, the UE can transmitthe P-CSI for the unlicensed CC in the PUSCH of the licensed CC.

[UCI Transmission Mode 2]

In UCI transmission mode 2, the UE may transmit P-CSI pertaining to theunlicensed CC only in the PUSCH of a specific cell or in the PUSCHs ofall the LAA SCells that are scheduled. Here, the specific cell may be,for example, the cell where a predetermined cell-related indicator isthe smallest among the LAA SCells scheduled. The predetermined indicatormay be a cell ID, a physical cell ID, a virtual cell ID, a cell index(for example, an SCell index, an index that is unique to LAA SCells,etc.), or other indicators.

FIG. 6 provide diagrams to illustrate examples of transmission controlin accordance with UCI transmission mode 2. FIG. 6A illustrates a casewhere PUCCH+PUSCH simultaneous transmission is not possible, and FIG. 6Billustrates a case where PUCCH+PUSCH simultaneous transmission ispossible. In FIG. 6, regardless of whether or not PUCCH+PUSCHsimultaneous transmission is possible, P-CSI for all unlicensed CCs istransmitted in the PUSCH of LAA SCell_(i).

[UCI Transmission Mode 3]

In UCI transmission mode 3, the UE controls the transmission of UCIusing a newly defined operation. First, one specific LAA SCell isselected as a special LAA SCell for transmitting UCI. This special LAASCell may be referred to as “XSCell,” for example.

The UE may select XSCell and report information that represents thisXSCell to the eNB. The report may be sent, for example, via higher layersignaling (for example, RRC signaling), physical layer signaling (UCI),or a combination of these. The UE may select XSCell based on the historyof LBT results, for example.

Also, the eNB may select XSCell and report information that representsthis XSCell to the UE. The report may be sent, for example, via higherlayer signaling (for example, RRC signaling), physical layer signaling(for example, DCI such as a UL grant), or a combination of these.

The eNB may select XSCell using or based on, for example, one or acombination of following (a) to (d):

(a) uniform and random selection;

(b) A/Ns for each carrier;

(c) history of UL-LBT results reported from the UE; and

(d) when type-B multicarrier LBT is used for UL-LBT, a CC that isselected to implement LBT category 4 (LBT to which random backoff isapplied) and XSCell are associated.

The UE transmits A/Ns and/or P-CSI for the unlicensed CC only in thePUSCH of XSCell based on LBT. Here, if PUCCH+PUSCH simultaneoustransmission is not possible, the UE transmits the UCI (A/Ns and/orP-CSI) in the unlicensed CC only at timings where there is no PUCCHtransmission in the licensed CC. On the other hand, if PUCCH+PUSCHsimultaneous transmission is possible, the UE transmits the UCI in theunlicensed CC, regardless of the licensed CC.

FIG. 7 provide diagrams, illustrating examples of transmission controlaccording to UCI transmission mode 3. FIG. 7A illustrates a case wherePUCCH+PUSCH simultaneous transmission is not possible, and FIG. 7Billustrates a case where PUCCH+PUSCH simultaneous transmission ispossible. XSCell is LAA SCell_(i) in FIG. 7A and LAA SCell_(i+1) in FIG.7B.

In FIG. 7A, at a timing where there is no PUCCH transmission in thelicensed CC, the unlicensed CC's A/N is transmitted in XSCell, and thiscell's A-CSI (A-CSI_(i)) of the cell is transmitted in LAA SCell Notethat the UE gives priority to PUCCH at a timing where there is PUCCHtransmission in the licensed CC.

In FIG. 7B, the UE transmits the UCI of the licensed CC in the licensedCC (PCell or PUCCH cell) and transmits A/N and P-CSI for the unlicensedCC in the PUSCH of XSCell. The UE transmits the unlicensed CC's A-CSI ina measurement-triggered cell.

In UCI transmission mode 3, the UE may retain the UCI (for example, A/Nand P-CSI) for the unlicensed CC for a predetermined period (which maybe referred to as “UCI retention period (time window for UCIretention),” “first retention period (first UCI retention period relatedto PUSCH),” and so on). When the opportunity to transmit PUSCH arrivesduring the first retention period, the UE transmits all the UCI that hasbeen retained all together. Meanwhile, the UE discards the UCI that haspassed the first retention period.

The first retention period may be defined as a period in whichtransmission of certain UCI (for example, A/N bit) in PUSCH is valid.Also, the first retention period may be pre-defined in the specificationusing fixed values, or may be reported from the eNB by higher layersignaling (for example, RRC signaling), physical layer signaling (DCIsuch as a DL grant), or a combination of these.

Note that the UE retains an A/N during the first retention period, evenwhen no uplink resource-scheduling UL grant is received. The firstretention period may start from the first time resource (for example,TTI) of XSCell's PUSCH where UCI may be transmitted, or start from theTTI where given UCI is generated (for example, a TTI where a DL signalis received).

Also, even when a UL grant is received, there is a possibility that LBTwill fail and UCI transmission will be delayed. Therefore, in UCItransmission mode 3, the UE may retain the UCI (for example, A/N andP-CSI) for the unlicensed CC for a predetermined period (also referredto as “time window for UCI transmission,” “second retention period(second UCI retention period on PUSCH),” etc.), which is different fromthe above-mentioned UCI retention period.

The second retention period may be defined as a period which starts fromthe first time resource (for example, TTI) of XSCell's PUSCH where givenUCI may be transmitted, and in which this UCI can be transmitted inXSCell's PUSCH. Also, the second retention period may be pre-defined inthe specification using fixed values, or may be reported from the eNB byhigher layer signaling (for example, RRC signaling), physical layersignaling (DCI such as a DL grant), or a combination of these.

Note that, as for the retention period for predetermined UCI (forexample, A/N), the one with the larger value between the first retentionperiod (for example, Y ms) and the second retention period (for example,X ms) may be used, or it is equally possible to use the retention perioduntil a UL grant is received as the first retention period, and use theretention period after a UL grant is received (after a transmissionstarting timing based on the receipt of a UL grant) as the secondretention period.

Furthermore, either the retention period until a UL grant is received orthe retention period after a UL grant is received may be set as thefirst retention period (or second retention period). In this case, theUE may exert control so that, when a UL grant is received, the time thathas passed since the retention of each retained UCI started is reset.

Note that, once UCI is transmitted successfully, the UE may discard thisUCI even during the UCI retention period. On the other hand, even afterUCI is transmitted successfully, the UE may retain this UCI during theUCI retention period.

Also, the UCI retention period, the first retention period, the secondretention period and others may be individually configured/defined foreach type of UCI.

FIG. 8 is a diagram to illustrate an example of the UCI retentionoperation in UCI transmission mode 3 according to the third embodiment.FIG. 8 illustrates downlink signals (DL Tx) received by the UE, ULgrants received by the UE, uplink resources for the PUSCH of XSCell, andUCIs (A/Ns) that are transmitted based on UL grants.

FIG. 8 assumes a TTI duration of 1 ms, but the TTI duration is notlimited to this. The same applies to FIG. 9 and FIG. 10 below.

In FIG. 8, the UE receives downlink signals (downlink data) in twelveconsecutive TTIs. an A/N (A/N_(j)) is generated in response to thereceipt of a downlink signal in the j-th TTI, and retained. In this way,every time the UE receives a downlink signal, the UE generates an A/N inresponse, and retains this. In FIG. 8, the UCI retention period (X) isconfigured to 9 ms. Consequently, each A/N_(j) is discarded after it isretained for 9 ms.

Also in FIG. 8, in TTIs where the UE receives downlink data, the UE alsoreceives UL grants that schedule XSCell's uplink transmission. In FIG.8, each UL grant schedules transmission of a transport block in onesubframe (single-subframe scheduling).

The UE performs LBT-based UL transmission (including transmission ofUCI) in XSCell a predetermined period of time (for example, 4 ms) aftera UL grant is received. In this example, even UCI that has beensuccessfully transmitted is retained during the UCI retention period.The same applies to the examples of FIG. 9 and FIG. 10.

In this example, the UE can transmit UCI as long as the UCI retentionperiod (X) continues, so that the possibility that the UE can transmiteach UCI can be improved.

FIG. 9 is a diagram to illustrate another example of the UCI retentionoperation in UCI transmission mode 3 according to the third embodiment.FIG. 9 illustrates downlink signals (DL Tx) received by the UE, ULgrants received by the UE, uplink resources for the PUSCH of XSCell, andUCIs (A/Ns) that are transmitted based on UL grants.

In FIG. 9, the UE receives downlink signals (downlink data) in twelveconsecutive TTIs, as in the example of FIG. 8. In FIG. 9, the firstretention period (Y) is configured to 6 ms, and the second retentionperiod (X) is configured to 9 ms. Consequently, each A/N_(j) isdiscarded after it is retained for 9 ms.

Furthermore, in FIG. 9, in the TTIs where the sixth and twelfth downlinksignals are transmitted, UL grants are transmitted. In FIG. 9, each ULgrant schedules the transmission of transport blocks in multiplesubframes (multi-subframe scheduling).

In this example, a UL grant commands the transmission of UL subframes ina number of TTIs to match second retention period, so that it ispossible to improve the possibility that the UE can transmit each UCI.

FIG. 10 is a diagram to illustrate yet another example of the UCIretention operation in UCI transmission mode 3 according to the thirdembodiment. FIG. 10 illustrates downlink signals (DL Tx) received by theUE, UL grants received by the UE, UCIs (A/Ns) that are retained fortransmission (awaiting transmission), UCIs (A/Ns) that are transmittedbased on UL grants.

FIG. 10 illustrates an example in which the eNB tries to transmitdownlink signals (downlink data) in twelve consecutive TTIs, and inwhich the eNB nevertheless fails to transmit some of the downlinksignals cannot be transmitted because the LBT result indicated a busystate. In FIG. 10, the first retention period (Y) is configured to 6 ms,and the second retention period (X) is not configured. Consequently,each A/N_(j) is discarded when 6 ms pass without receiving a UL grant,or when 6 ms pass after transmission is ready.

At the transmission timing based on the first UL grant illustrated inFIG. 10, A/N₁ to A/N₄ are retained as UCIs that can be transmitted.Also, at the transmission timing based on the second UL grantillustrated in FIG. 10, A/N₄ to A/N₆ are retained.

As explained in this example, even when UL grants cannot be received, itis still possible to improve the possibility that the UE, where thefirst retention period (Y) is configured, can transmit each UCI.

Note that the UCIs to retain are not limited to A/N and P-CSI. Forexample, the transmission of at least one of A/N, P-CSI, A-CSI and SRmay be controlled based on the first retention period and/or the secondretention period.

[Control Signal for UCI Transmission Mode]

It may be possible to use a UL grant, a PDCCH that is transmitted in acommon search space (common PDCCH) and so on, as a control signal forconfiguring the UCI transmission modes described in the third embodimentin the UE.

For example, information about UCI transmission modes may be reportedusing a UL grant. As this information, for example, two-bit informationto represent UCI transmission modes 0 to 3 may be used.

Furthermore, information for specifying the special LAA SCell (XSCell)for UCI transmission in UCI transmission mode 3 may be reported using aUL grant. For this information, information of a predetermined number ofbits may be used (where the predetermined number is, for example, thenumber of LAA SCells, the maximum number of LAA SCells, etc.).

Furthermore, information about the first retention period and/or thesecond retention period in UCI transmission mode 3 may be reported in acommon PDCCH (for example, DCI format 1C). The common PDCCH may betransmitted in the PCell, or may be transmitted in an SCell of alicensed CC and/or an LAA SCell.

Note that, in order to command these pieces of UCI mode-related controlinformation, new fields may be set forth in DCI formats, or may replaceexisting fields (for example, the resource allocation field) and beused.

Fourth Embodiment

With a fourth embodiment of the present invention, the codebook size(also referred to as “CBS,” “HARQ codebook size,” etc.) for use whenHARQ-ACK transmission is carried out in LAA SCells will be explained.Note that, although PUCCH transmission is not configured in LAA SCells(PUCCH on LAA SCell) in the case described below, UCI such as HARQ-ACKis transmitted in PUSCH. However, the present embodiment is not limitedto this, and can also be applied to cases where PUCCH transmission isperformed.

When sending HARQ-ACK in response to DL transmission, the user terminaltransmits the HARQ-ACK in a predetermined codebook size (also referredto as “ACK/NACK bit sequence,” “A/N bit size,” etc.). In existingsystems, the codebook size of HARQ-ACK (ACK/NACK bit sequence) to betransmitted in PUCCH is determined semi-statically based on informationabout the number of CCs reported by higher layer signaling.

When FDD is used, the overall A/N bit size is determined based on thenumber of CCs configured by RRC signaling, and based on TM (TransmissionMode), which indicates whether or not MIMO (Multiple Input MultipleOutput) is applicable in each CC. In a given DL subframe, if a DLassignment is detected in at least one SCell, the user terminal feedsback A/Ns in response to all the CCs that are configured, in the ULsubframe that comes a predetermined period later (for example, 4 mslater).

When TDD is used, in addition to the above case of using FDD, theoverall size of the A/N bit sequence to transmit in PUCCH is determinedbased on the number of DL subframes that pertain to A/N per UL subframe.

Meanwhile, as mentioned above, when A/N transmission is controlled sothat an A/N is retained for a predetermined period of time in LAASCells, how to configure the codebook size is the problem. Sinceexisting systems do not assume that A/Ns are retained, if existingmethods are applied on an as-is basis, it may not be possible toconfigure the codebook size adequately. In this way, another problemwhich the present invention addresses is how to appropriately configurethe codebook size when performing HARQ-ACK transmission in LAA SCells.

So, the present inventors have come up with the idea of determining thecodebook size of HARQ-ACK by taking into account the retention period ofA/Ns, when transmitting HARQ-ACK in LAA SCells. Hereinafter, the casewhere the codebook size is fixedly configured (fixed codebook size) andthe case where the codebook size is dynamically configured (dynamiccodebook size) when HARQ-ACK transmission is performed in LAA SCellswill be described.

According to the fourth embodiment, the user terminal transmits A/Ns(retransmission control information) in response to downlink signals inLAA SCells (carriers where listening is performed before transmission).The user terminal configures the codebook size to use to transmit an A/Nbased on the time the user terminal retains this A/N.

[Fixed Codebook Size]

When using a fixed codebook size, the user terminal may configure afixed codebook size based on the period the A/N is retained in the userterminal (A/N retention period). Here, the A/N retention period may beat least one of the period A/N is retained, starting from a TTI that isscheduled by a UL grant (second retention period (X)), and the period inwhich an A/N in response to a downlink signal is retained, starting fromthe TTI in which the downlink signal is received (first retention period(Y)).

The user terminal retains an A/N for the second retention period (X),which starts from a TTI scheduled by a UL grant. Therefore, even whenthe user terminal fails listening in this scheduled TTI, if the userterminal succeeds in listening in a subsequent TTI within the secondretention period (X), the user terminal can transmit the A/N. After thesecond retention period (X) is over, the user terminal discards the A/N.

Also, the user terminal retains an A/N for the first retention period(Y) from a TTI in which a downlink signal is received. Consequently,even when the user terminal does not receive a UL grant in this TTI inwhich a downlink signal is received (downlink data, a downlink datachannel (for example, PDSCH (Physical Downlink Shared Channel)), etc.),if the user terminal successfully receives a UL grant in a subsequentTTI within the first retention period (Y), the user terminal cantransmit the A/N in the TTI scheduled by this UL grant. When the firstretention period (Y) is over, the user terminal discards the A/N.

Note that, when the first retention period (Y) is equal to the TTIduration (for example 1 ms), this may be interpreted to mean that thefirst retention period (Y) is not configured. In this case, if the userterminal does not receive a UL grant in a TTI in which a downlink signalwas received, the user terminal cannot transmit an A/N in response tothe downlink signal.

Also, the user terminal may configure the fixed codebook size based onthe number of CCs (cells), in addition to the above-described A/Nretention period (at least one of the first retention period (Y) and thesecond retention period (X)). Here, the number of CCs has to be thenumber of cells (CCs) where A/Ns need to be transmitted in response todownlink signals, but is not limited to the number of LAA SCells or thenumber of CCs configured in the user terminal. Also, the number of CCsmay be the number of CCs in a UCI cell group.

For example, the user terminal may configure a fixed codebook size basedon following equation 1:

CBS=[X/Y]·Y·N  (Equation 1)

where X is the second retention period described above, Y is the firstretention period described above, and N is the number of cells (CC)where A/Ns are generated in response to downlink signals. Note thatequation 1 is simply an example, and this is by no means limiting.Various parameters that are not indicated in equation 1 may be takeninto account.

Also, although above X, Y and N are configured via higher layersignaling, these may be specified through physical layer signaling, ordetermined by a combination of higher layer signaling and physical layersignaling. Also, the CBS itself may be configured via higher layersignaling, or may be specified through physical layer signaling.

FIG. 17 is a diagram to illustrate an example of the method ofdetermining the codebook size according to the fourth embodiment. FIG.17 illustrates downlink signals (DL Tx) received by the UE, UL grantsreceived by the UE, uplink resources for the PUSCH of XSCell, UCIs(A/Ns) that are transmitted based on UL grants, A/Ns retained in eachTTI based on the first retention period (Y), and A/Ns retained in eachTTI based on the second retention period (X).

In FIG. 17, the TTI duration is 1 ms, but the TTI duration is notlimited to this. The same applies to FIG. 18 and FIG. 19 below.Furthermore, although, in FIG. 17, a UL grant schedules UL transmissionin the TTI that comes four TTIs later, UL transmission to be scheduledby a UL grant is not limited to four TTIs later.

Also, although FIG. 17 illustrates a case of single-subframe scheduling,in which UL transmission is scheduled in a single subframe by a UL grantin a single subframe, multi-subframe scheduling can be applied as well,in which UL transmission is scheduled in a plurality of subframes bythat UL grant.

Also, in FIG. 17, the first retention period (Y) is configured to 6 ms,and the second retention period (X) is configured to 9 ms. Note that theconfiguration values of the first retention period (Y) and the secondretention period (X) are not limited to these. The configuration valuesof the first retention period (Y) and the second retention period (X)may each be n (n 1) times the TTI duration. For example, if the firstretention period (Y) is not configured (in the event control is exertedso that, unless a UL grant is received in a TTI in which a downlinksignal is received, no A/N is transmitted in response to this downlinksignal), Y=TTI duration (for example, 1 ms) may be used.

In addition, in FIG. 17, the number (N) of cells (CCs) where A/Ns aregenerated in response to downlink signals is configured to 1, but thisis not limiting. In FIG. 17, the fixed codebook size determined usingabove equation 1 is 12 (=2·6·1).

In FIG. 17, the user terminal receives downlink signals (downlink data)in 18 consecutive TTIs. When a downlink signal is received in the j-thTTI, A/N_(j) is generated in response to this downlink signal. The userterminal retains the generated A/N_(j) for the first retention period(Y) (here, for 6 ms). For example, A/N₁ in response to the downlinksignal of the first TTI is retained from the first TTI to the sixth TTI,and discarded if no UL grant is received by the sixth TTI.

Thus, A/N_(j) in response to the downlink signal of the j-th TTI isretained from the j-th TTI to the j+(Y−1)-th TTI. A/N_(j) is discardedunless a UL grant is received before the j+(Y−1)-th TTI. On the otherhand, when a UL grant is received by the j+(Y−1)-th TTI, A/N_(j) istransmitted using the PUSCH scheduled by this UL grant.

In FIG. 17, when a UL grant is received in the sixth TTI, A/N₁ to A/N₆in response to the downlink signals of the first to sixth TTIs areretained based on the first retention period (Y), so that transmissionof A/N₁ to A/N₆ is attempted in the tenth TTI scheduled by the UL grant.Meanwhile, the user terminal may not succeed in LBT in or immediatelybefore the tenth TTI. So, the user terminal retains A/N₁ to A/N₆ for thesecond retention period (X) (here, for 9 ms) from the tenth TTIscheduled by the UL grant. In FIG. 17, since LBT succeeds in orimmediately before the tenth TTI, A/N₁ to A/N₆ are transmitted in thistenth TTI, using six bits out of the twelve bits of the codebook. Inthis case, the remaining six bits that are not used may be, for example,configured in default values (for example, NACK).

Also, at the time a UL grant is received in the twelfth TTI, A/N 7 toA/N₁₂ in response to the downlink signals of the seventh to twelfth TTIare retained based on the first retention period (Y). Furthermore, inthe sixteenth TTI scheduled by the UL grant, in addition to A/N₇ toA/N₁₂ above, A/N₁ to A/N₆ in response to the downlink signals of thefirst to sixth TTIs are retained based on the second retention period(X). Therefore, in the sixteenth TTI, A/N₁ to A/N₁₂ are transmittedusing all bits of the twelve-bit codebook.

Also, at the time a UL grant is received at the eighteenth TTI, A/N₁₃ toA/N₁₈ in response to the downlink signals of the thirteenth toeighteenth TTIs are retained based on the first retention period (Y).Furthermore, in the sixteenth TTI scheduled by the UL grant, in additionto A/N₁₃ to A/N₁₈ above, A/N₇ to A/N₁₂ in response to the downlinksignals of the seventh to twelfth TTIs are retained based on the secondretention period (X). Accordingly, in the twentieth TTI, A/N₇ to A/N₁₈are transmitted using all bits of the twelve-bit codebook.

As described above, when the codebook size of each TTI is set in a fixedsize that is equal to the maximum possible number of A/Ns, it ispossible to simplify the control of the codebook size in the userterminal.

[Dynamic Codebook Size]

When dynamically changing the codebook size, the codebook size isdetermined taking the A/N retention period into account (for example,the second retention period (X)). For example, when UL transmission isperformed in a given subframe (SF #n), the codebook size is controlledbased on whether or not there is a UL subframe in a range of apredetermined period going backward from this SF #n. The UL subframehere refers to a UL subframe in which at least HARQ-ACK has beentransmitted (including cases where transmission is not allowed due toLBT results). Also, the predetermined period can be a range that takesinto account the A/N retention period (for example, X−1 or less). Ofcourse, X−1 is not limiting.

The user terminal changes the codebook size depending on whether or notthere is a UL subframe (for example, SF #m) in which HARQ-ACK istransmitted, within a range that goes (X−1) ms backward from SF #n whereHARQ-ACK is transmitted. To be more specific, when there is a ULsubframe (SF #m) in which HARQ-ACK is transmitted within the range backto (X−1) ms before SF #n in which HARQ-ACK transmission is performed,the user terminal determines the codebook size of SF #n, by additionallytaking into account the codebook size of HARQ-ACK of SF #m. Note thatthere may be more than one SF #m.

In this case, the user terminal can determine the codebook size of SF #nregardless of the result of LBT in SF #m (based only on the position ofSF #m). Alternatively, the codebook size in SF #n may be controlled,taking into account the result of UL transmission (LBT result) in SF #m.For example, a structure may be employed here in which, to decide thecodebook size in SF #n when an A/N is successfully transmitted in SF #m(LBT idle), the codebook size of SF #m is not taken into consideration.

If, on the other hand, SF #m is not present within a range of (X−1) msgoing back from SF #n, the codebook size of SF #n is determined withoutconsidering the codebook size of other UL subframes. Note that althoughthe second retention period (X) described above is assumed as theretention period here, this is not limiting. The above-described firstretention period (Y) may be taken into account.

FIG. 18 illustrates an example where the codebook size is dynamicallychanged taking the A/N retention period into account. In the caseillustrated in FIG. 18, A/Ns in response to the DL signals (for example,PDSCH) transmitted in SF #2 to SF #5 are transmitted in SF #9, and A/Nsin response to the DL signals transmitted in SF #11 to SF #14 aretransmitted in SF #17.

Furthermore, in FIG. 18, the A/N transmission (codebook size, etc.) ineach UL subframe SF #9 and #17 is controlled based on DAIs (DownlinkAssignment Indicators (Indices)) included in DL signals. As for the DAIsto be included in DL signals (for example, DCI), a counter DAI (alsoreferred to as “C-DAI,” and so on), a total DAI (also referred to as a“T-DAI” and so on), and others are stipulated.

The counter DAI is information (count value) that is used to count theDL signals that are scheduled (in FDD, this corresponds to the number ofCCs). The total DAI is information that indicates the number of DLsignals that are scheduled (in FDD, this corresponds to the number ofCCs). In the radio base station, the counter DAI and the total DAI areincluded in each CC's downlink control information and reported to theuser terminal. Note that the counter DAI and/or the total DIA can bespecified using two bits.

The user terminal can determine the number of scheduled DL signals(codebook size) based on the reported total DAI and can also determinethe A/N for each DL signal based on the counter DAI.

For example, in FIG. 18, the DCI of each DL signal transmitted in SF #2to SF #5 includes a different counter DAI (here, 1 to 8) and a commontotal DAI (here, 8). Here, since no DL signal with a counter DAI of 5 isreceived, the user terminal determines that the user terminal has failedto receive the DL signal with the counter DAI=5. The user terminaldetermines the A/N and codebook size (here, 8) in each DL subframe basedon the counter DAI and the total DAI, and transmits multiple A/Ns in SF#9.

Furthermore, in FIG. 18, the DCI of each DL signal transmitted in SF #11to SF #14 includes a different counter DAI (here, 1 to 7) and a commontotal DAI (here, 7). Here, since no DL signal with a counter DAI of 7 isreceived, the user terminal can determine that the user terminal hasfailed to receive the DL signal with the counter DAI=7. The userterminal determines the A/N and codebook size (here, 7) of each DLsubframe based on the counter DAI and the total DAI, and transmitsmultiple A/Ns in SF #17.

Thus, by determining the codebook size based on the total DAI, it ispossible to dynamically change the codebook size taking into account thenumber of DL signals that are scheduled.

Furthermore, according to the present embodiment, when there is a ULsubframe (SF #m) within a range of (X−1) ms going backward from SF #nwhere HARQ-ACK is transmitted, the codebook size of SF #n is determinedby additionally taking into account the codebook size (for example,total DAI) of SF #m. For example, assume the case where the HARQ-ACKcodebook size in the UL subframe of SF #17 in FIG. 18 is determined.

In this case, the user terminal checks whether or not a UL subframe ispresent in a range of a predetermined period (for example, X−1 or less)backward from SF #17. For example, if X=9 is configured, the userterminal checks whether or not a UL subframe is present within a rangeof eight subframes backward from SF #17 (that is, in SFs #9 to #16). InFIG. 18, since there is a UL subframe in SF #9, the user terminaldetermines the codebook size in SF #17 taking into consideration thecodebook size (for example, the total DAI) in SF #9, and carries out A/Ntransmission accordingly.

To be more specific, the user terminal combines the codebook size in SF#9 (here, 8) and the codebook size (here, 7) of the A/Ns transmitted inresponse to the DL signals of SFs #11 to #14, and uses the resultingvalue (CBS=8+7) as the codebook size for SF #17. Then, the user terminalfeeds back A/Ns in response to the DL signals of SFs #2 to #5 and A/Nsin response to the DL signals of SFs #11 to #14 using this codebooksize.

On the other hand, if, as illustrated in FIG. 19, there is no ULsubframe (SF #m) within a range of (X−1) ms going backward, from SF #nin which HARQ-ACK is transmitted, the user terminal determines thecodebook size for SF #n without considering the codebook size in SF #m.For example, assume the case where the codebook size in the UL subframeof SF #22 in FIG. 19 is determined. Note that, FIG. 19 is equivalent toa case where the subframe of SF #17 in FIG. 18 is replaced by SF #22.

In this case, the user terminal checks whether or not a UL subframe ispresent within a range of a predetermined period (for example, X−1 orless) backward from SF #22. For example, when X=9 is configured, theuser terminal checks whether or not a UL subframe is present within arange of eight subframes backward from SF #22 (that is, in SFs #14 to#21). In FIG. 19, the UL subframe that is configured before SF #22 is SF#9 (which is beyond X−1 ms), so that the user terminal determines thecodebook size of SF #22 without considering the codebook size in SF #9,and performs A/N transmission accordingly.

To be more specific, the user terminal determines the codebook size(here, 7) of the A/Ns to transmit in response to the DL signals of SFs#11 to #14 as the codebook size in SF #22. Then, the user terminal feedsback A/Ns in response to the DL signals of SFs #11 to #14 using thiscodebook size.

That is, in the case illustrated in FIG. 19, since the A/Ns transmittedin SF #9 (the A/Ns transmitted in response to the DL signals of SFs #2to #5) are not retained in SF #22, the user terminal performs A/Ntransmission without takes into consideration the A/Ns in SF #9. In thisway, the codebook size is changed dynamically by taking into account theperiod for retaining A/Ns, so that it is possible to prevent theopportunities for transmitting A/Ns from reducing due to LBT results(LBT busy), and, furthermore, prevent the overhead of the codebook sizefrom increasing.

HARQ-ACK transmission in LAA SCells is assumed to be configured so thatonly A/Ns that have failed to be transmitted due to “LBT busy” aretransmitted at different timings than in existing system (that is, anA/N, once transmitted successfully, is not transmitted at a timingdifferent from the existing one). By means of this configuration, thedynamic codebook size, which has been described above, can be suitablyapplied.

(Radio Communication System)

Now, the structure of the radio communication system according to oneembodiment of the present invention will be described below. In thisradio communication system, the radio communication method according toone and/or a combination of the above-described embodiments of thepresent invention is employed.

FIG. 11 is a diagram to illustrate an example of a schematic structureof a radio communication system according to one embodiment of thepresent invention. A radio communication system 1 can adopt carrieraggregation (CA) and/or dual connectivity (DC) to group a plurality offundamental frequency blocks (component carriers) into one, where theLTE system bandwidth constitutes 1 unit. Also, the radio communicationsystem 1 has a radio base station (for example, an LTE-U base station)that is capable of using unlicensed bands.

Note that the radio communication system 1 may be referred to as “SUPER3G,” “LTE-A” (LTE-Advanced), “IMT-Advanced,” “4G” (4th generation mobilecommunication system), “5G” (5th generation mobile communicationsystem), “FRA” (Future Radio Access) and so on.

The radio communication system 1 illustrated in FIG. 11 includes a radiobase station 11 that forms a macro cell C1, and radio base stations 12(12 a to 12 c) that form small cells C2, which are placed within themacro cell C1 and which are narrower than the macro cell C1. Also, userterminals 20 are placed in the macro cell C1 and in each small cell C2.For example, a mode may be possible in which the macro cell C1 is usedin a licensed band and the small cells C2 are used in unlicensed bands(LTE-U). Also, a mode may be also possible in which part of the smallcells is used in a licensed band and the rest of the small cells areused in unlicensed bands.

The user terminals 20 can connect with both the radio base station 11and the radio base stations 12. The user terminals 20 may use the macrocell C1 and the small cells C2, which use different frequencies, at thesame time, by means of CA or DC. For example, it is possible to transmitassist information (for example, the DL signal configuration) related toa radio base station 12 (which is, for example, an LTE-U base station)that uses an unlicensed band, from the radio base station 11 that uses alicensed band to the user terminals 20. Furthermore, a structure may beemployed here in which, when CA is applied between a licensed band andan unlicensed band, 1 radio base station (for example, the radio basestation 11) controls the scheduling of licensed band cells andunlicensed band cells.

Note that it is equally possible to adopt a structure in which a userterminal 20 connects with the radio base stations 12, without connectingwith the radio base station 11. For example, it is possible to adopt astructure in which a radio base station 12 that uses an unlicensed bandestablishes a stand-alone connection with a user terminal 20. In thiscase, the radio base station 12 controls the scheduling of unlicensedband cells.

Between the user terminals 20 and the radio base station 11,communication can be carried out using a carrier of a relatively lowfrequency band (for example, 2 GHz) and a narrow bandwidth (referred toas, for example, an “existing carrier,” a “legacy carrier” and so on).Meanwhile, between the user terminals 20 and the radio base stations 12,a carrier of a relatively high frequency band (for example, 3.5 GHz, 5GHz and so on) and a wide bandwidth may be used, or the same carrier asthat used in the radio base station 11 may be used. Note that thestructure of the frequency band for use in each radio base station is byno means limited to these.

A structure may be employed here in which wire connection (for example,means in compliance with the CPRI (Common Public Radio Interface) suchas optical fiber, the X2 interface and so on) or wireless connection isestablished between the radio base station 11 and the radio base station12 (or between two radio base stations 12).

The radio base station 11 and the radio base stations 12 are eachconnected with higher station apparatus 30, and are connected with acore network 40 via the higher station apparatus 30. Note that thehigher station apparatus 30 may be, for example, access gatewayapparatus, a radio network controller (RNC), a mobility managemententity (MME) and so on, but is by no means limited to these. Also, eachradio base station 12 may be connected with the higher station apparatus30 via the radio base station 11.

Note that the radio base station 11 is a radio base station having arelatively wide coverage, and may be referred to as a “macro basestation,” a “central node,” an “eNB” (eNodeB), a “transmitting/receivingpoint” and so on. Also, the radio base stations 12 are radio basestations having local coverages, and may be referred to as “small basestations,” “micro base stations,” “pico base stations,” “femto basestations,” “HeNBs (Home eNodeBs),” “RRHs (Remote Radio Heads),”“transmitting/receiving points” and so on. Hereinafter the radio basestations 11 and 12 will be collectively referred to as “radio basestations 10,” unless specified otherwise. Also, it is preferable toconfigure radio base stations 10 that use the same unlicensed band on ashared basis to be synchronized in time.

The user terminals 20 are terminals that support various communicationschemes such as LTE, LTE-A and so on, and may be either mobilecommunication terminals or stationary communication terminals.

In the radio communication system 1, as radio access schemes, OFDMA(Orthogonal Frequency Division Multiple Access) is applied to thedownlink and SC-FDMA (Single-Carrier Frequency Division Multiple Access)is applied to the uplink.

OFDMA is a multi-carrier communication scheme to perform communicationby dividing a frequency bandwidth into a plurality of narrow frequencybandwidths (subcarriers) and mapping data to each subcarrier. SC-FDMA isa single-carrier communication scheme to mitigate interference betweenterminals by dividing the system bandwidth into bands formed with one orcontinuous resource blocks per terminal, and allowing a plurality ofterminals to use mutually different bands. Note that the uplink anddownlink radio access schemes are by no means limited to the combinationof these.

In the radio communication system 1, a downlink shared channel (PDSCH:Physical Downlink Shared CHannel), which is used by each user terminal20 on a shared basis, a broadcast channel (PBCH: Physical BroadcastCHannel), downlink L1/L2 control channels and so on are used as downlinkchannels. User data, higher layer control information and SIBs (SystemInformation Blocks) are communicated in the PDSCH. Also, the MIB (MasterInformation Block) is communicated in the PBCH.

The downlink L1/L2 control channels include a PDCCH (Physical DownlinkControl CHannel), an EPDCCH (Enhanced Physical Downlink ControlCHannel), a PCFICH (Physical Control Format Indicator CHannel), a PHICH(Physical Hybrid-ARQ Indicator CHannel) and so on. Downlink controlinformation (DCI), including PDSCH and PUSCH scheduling information, iscommunicated by the PDCCH. The number of OFDM symbols to use for thePDCCH is communicated by the PCFICH. HARQ delivery acknowledgementsignals (ACK/NACK) in response to the PUSCH are communicated by thePHICH. The EPDCCH is frequency-division-multiplexed with the PDSCH andused to communicate DCI and so on, like the PDCCH.

In the radio communication system 1, an uplink shared channel (PUSCH:Physical Uplink Shared CHannel), which is used by each user terminal 20on a shared basis, an uplink control channel (PUCCH: Physical UplinkControl CHannel), a random access channel (PRACH: Physical Random AccessCHannel) and so on are used as uplink channels. The PUSCH may bereferred to as an “uplink data channel.” User data and higher layercontrol information are communicated by the PUSCH. Also, downlink radioquality information (CQI: Channel Quality Indicator), deliveryacknowledgment information (ACK/NACK) and so on are communicated by thePUCCH. By means of the PRACH, random access preambles for establishingconnections with cells are communicated.

In the radio communication systems 1, cell-specific reference signals(CRSs), channel state information reference signals (CSI-RSs),demodulation reference signal (DMRSs) and so on are communicated asdownlink reference signals. Also, in the radio communication system 1,the measurement reference signal (SRS: Sounding Reference Signal), thedemodulation reference signal (DMRS) and so on are communicated asuplink reference signals. Note that the DMRS may be referred to as a“user terminal-specific reference signal (UE-specific ReferenceSignal).” Also, the reference signals to be communicated are by no meanslimited to these.

(Radio Base Station)

FIG. 12 is a diagram to illustrate an example of an overall structure ofa radio base station according to one embodiment of the presentinvention. A radio base station 10 has a plurality oftransmitting/receiving antennas 101, amplifying sections 102,transmitting/receiving sections 103, a baseband signal processingsection 104, a call processing section 105 and a communication pathinterface 106. Note that one or more transmitting/receiving antennas101, amplifying sections 102 and transmitting/receiving sections 103 maybe provided.

User data to be transmitted from the radio base station 10 to a userterminal 20 on the downlink is input from the higher station apparatus30 to the baseband signal processing section 104, via the communicationpath interface 106.

In the baseband signal processing section 104, the user data issubjected to transmission processes, including a PDCP (Packet DataConvergence Protocol) layer process, division and coupling of the userdata, RLC (Radio Link Control) layer transmission processes such as RLCretransmission control, MAC (Medium Access Control) retransmissioncontrol (for example, an HARQ (Hybrid Automatic Repeat reQuest)transmission process), scheduling, transport format selection, channelcoding, an inverse fast Fourier transform (IFFT) process and a precodingprocess, and the result is forwarded to each transmitting/receivingsections 103. Furthermore, downlink control signals are also subjectedto transmission processes such as channel coding and an inverse fastFourier transform, and forwarded to each transmitting/receiving section103.

Baseband signals that are precoded and output from the baseband signalprocessing section 104 on a per antenna basis are converted into a radiofrequency band in the transmitting/receiving sections 103, and thentransmitted. The radio frequency signals having been subjected tofrequency conversion in the transmitting/receiving sections 103 areamplified in the amplifying sections 102, and transmitted from thetransmitting/receiving antennas 101.

The transmitting/receiving sections 103 are capable oftransmitting/receiving UL/DL signals in unlicensed bands. Note that thetransmitting/receiving sections 103 may be capable oftransmitting/receiving UL/DL signals in licensed bands as well. Thetransmitting/receiving sections 103 can be constituted bytransmitters/receivers, transmitting/receiving circuits ortransmitting/receiving apparatus that can be described based on generalunderstanding of the technical field to which the present inventionpertains. Note that a transmitting/receiving section 103 may bestructured as a transmitting/receiving section in one entity, or may beconstituted by a transmitting section and a receiving section.

Meanwhile, as for uplink signals, radio frequency signals that arereceived in the transmitting/receiving antennas 101 are each amplifiedin the amplifying sections 102. The transmitting/receiving sections 103receive the uplink signals amplified in the amplifying sections 102. Thereceived signals are converted into the baseband signal throughfrequency conversion in the transmitting/receiving sections 103 andoutput to the baseband signal processing section 104.

In the baseband signal processing section 104, user data that isincluded in the uplink signals that are input is subjected to a fastFourier transform (FFT) process, an inverse discrete Fourier transform(IDFT) process, error correction decoding, a MAC retransmission controlreceiving process, and RLC layer and PDCP layer receiving processes, andforwarded to the higher station apparatus 30 via the communication pathinterface 106. The call processing section 105 performs call processing(such as setting up and releasing communication channels), manages thestate of the radio base stations 10 and manages the radio resources.

The communication path interface section 106 transmits and receivessignals to and from the higher station apparatus 30 via a predeterminedinterface. Also, the communication path interface 106 may transmit andreceive signals (backhaul signaling) with other radio base stations 10via an inter-base station interface (which is, for example, opticalfiber that is in compliance with the CPRI (Common Public RadioInterface), the X2 interface, etc.).

Note that the transmitting/receiving sections 103 transmit downlinkcontrol information (DCI) and/or higher layer signaling (for example,RRC signaling), which include PUCCH cell configuration information,information as to whether or not simultaneous PUCCH and PUSCHtransmission is possible, information about UCI transmission modes, andinformation about UCI retention periods, and so on, to the user terminal20 in licensed CCs and/or unlicensed CCs. In addition, thetransmitting/receiving sections 103 can receive the PUSCH from the userterminal 20 at least in unlicensed CCs.

FIG. 13 is a diagram to illustrate an example of a functional structureof a radio base station according to one embodiment of the presentinvention. Note that, although FIG. 10 primarily illustrates functionalblocks that pertain to characteristic parts of the present embodiment,the radio base station 10 has other functional blocks that are necessaryfor radio communication as well.

The baseband signal processing section 104 has a control section(scheduler) 301, a transmission signal generation section 302, a mappingsection 303, a received signal processing section 304 and a measurementsection 305. Note that these configurations have only to be included inthe radio base station 10, and some or all of these configurations maynot be included in the baseband signal processing section 104.

The control section (scheduler) 301 controls the whole of the radio basestation 10. Note that, when a licensed band and an unlicensed band arescheduled with 1 control section (scheduler) 301, the control section301 controls communication in licensed band cells and unlicensed bandcells. For the control section 301, a controller, a control circuit orcontrol apparatus that can be described based on common understanding ofthe technical field to which the present invention pertains can be used.

The control section 301, for example, controls the generation of signalsin the transmission signal generation section 302, the allocation ofsignals by the mapping section 303, and so on. Furthermore, the controlsection 301 controls the signal receiving processes in the receivedsignal processing section 304, the measurements of signals in themeasurement section 305, and so on.

The control section 301 controls the scheduling (for example, resourceallocation) of downlink data signals that are transmitted in the PDSCHand downlink control signals that are communicated in the PDCCH and/orthe EPDCCH. Also, the control section 301 controls the scheduling ofdownlink reference signals such as synchronization signals (the PSS(Primary Synchronization Signal) and the SSS (Secondary SynchronizationSignal)), the CRS, the CSI-RS, the DM-RS and so on.

Also, the control section 301 controls the scheduling of uplink datasignals transmitted in the PUSCH, uplink control signals transmitted inthe PUCCH and/or the PUSCH (for example, delivery acknowledgementsignals (HARQ-ACKs)), random access preambles transmitted in the PRACH,uplink reference signals and so on.

The control section 301 may control the transmission signal generationsection 302 and the mapping section 303 to transmit downlink signals(for example, PDCCH/EPDCCH) in carriers (for example, unlicensed CCs)where listening is performed before downlink transmission according tothe LBT result obtained in the measurement section 305.

The control section 301 may exert control so that UE capabilityinformation as to whether or not PF 4/5 are supported in at least one ofthe LBT carriers is obtained from the received signal processing section304, the PUCCH cell of LAA SCells is determined based on this capabilityinformation, and PUCCH cell configuration information pertaining to thiscell is transmitted to the user terminal 20.

The control section 301 may exert control so that information as towhether or not simultaneous transmission of PUCCH and PUSCH is possible,information about UCI transmission modes, information about UCIretention periods and so on are transmitted to the user terminal 20.

Furthermore, the control section 301 may determine in which cell theuser terminal transmits UCI based on the various pieces of informationtransmitted to the user terminal 20, and perform the receiving processand scheduling accordingly.

Furthermore, the control section 301 may control (determine) thecodebook size to use to transmit an A/N based on the time the A/N(retransmission control information) is retained in the user terminal 20(for example, at least one of the first retention time (Y) and thesecond retention time (X)). Furthermore, the control section 301 maycontrol the codebook size based on the number of CCs, in addition to thetime the A/N is retained.

The codebook size may be a fixed size that is uniquely determined ineach TTI (also referred to as “fixed codebook size,” as illustrated inFIG. 17), or may be a size that is dynamically changed (also referred toas “dynamic codebook size,” as illustrated in FIGS. 18 and 19). Thefixed codebook size may be equal to the maximum number of A/Ns that maybe transmitted in each TTI.

The transmission signal generation section 302 generates downlinksignals (downlink control signals, downlink data signals, downlinkreference signals and so on) based on commands from the control section301, and outputs these signals to the mapping section 303. Thetransmission signal generation section 302 can be constituted by asignal generator, a signal generating circuit or signal generatingapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains.

For example, the transmission signal generation section 302 generates DLassignments, which report downlink signal allocation information, and ULgrants, which report uplink signal allocation information, based oncommands from the control section 301. Also, the downlink data signalsare subjected to the coding process, the modulation process and so on,by using coding rates and modulation schemes that are determined basedon, for example, channel state information (CSI) from each user terminal20.

The mapping section 303 maps the downlink signals generated in thetransmission signal generation section 302 to predetermined radioresources based on commands from the control section 301, and outputsthese to the transmitting/receiving sections 103. The mapping section303 can be constituted by a mapper, a mapping circuit or mappingapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains.

The received signal processing section 304 performs receiving processes(for example, demapping, demodulation, decoding and so on) of receivedsignals that are input from the transmitting/receiving sections 103.Here, the received signals include, for example, uplink signalstransmitted from the user terminals 20 (uplink control signals, uplinkdata signals, uplink reference signals and so on). For the receivedsignal processing section 304, a signal processor, a signal processingcircuit or signal processing apparatus that can be described based ongeneral understanding of the technical field to which the presentinvention pertains can be used.

The received signal processing section 304 outputs the decodedinformation acquired through the receiving processes to the controlsection 301. For example, when a PUCCH to contain an HARQ-ACK isreceived, the received signal processing section 304 outputs thisHARQ-ACK to the control section 301. Also, the received signalprocessing section 304 outputs the received signals, the signals afterthe receiving processes and so on, to the measurement section 305.

The measurement section 305 conducts measurements with respect to thereceived signals. The measurement section 305 can be constituted by ameasurer, a measurement circuit or measurement apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains.

The measurement section 305 executes LBT in a carrier where LBT isconfigured (for example, an unlicensed band) based on commands from thecontrol section 301, and outputs the results of LBT (for example,judgments as to whether the channel state is free or busy) to thecontrol section 301.

Also, the measurement section 305 may measure, for example, the receivedpower (for example, RSRP (Reference Signal Received Power)), thereceived signal strength (for example, RSSI (Received Signal StrengthIndicator)), the received quality (for example, RSRQ (Reference SignalReceived Quality)) and the channel states of the received signals. Themeasurement results may be output to the control section 301.

(User Terminal)

FIG. 14 is a diagram to illustrate an example of an overall structure ofa user terminal according to one embodiment of the present invention. Auser terminal 20 has a plurality of transmitting/receiving antennas 201,amplifying sections 202, transmitting/receiving sections 203, a basebandsignal processing section 204 and an application section 205. Note thatone or more transmitting/receiving antennas 201, amplifying sections 202and transmitting/receiving sections 203 may be provided.

Radio frequency signals that are received in the transmitting/receivingantennas 201 are amplified in the amplifying sections 202. Thetransmitting/receiving sections 203 receive the downlink signalsamplified in the amplifying sections 202. The received signals aresubjected to frequency conversion and converted into the baseband signalin the transmitting/receiving sections 203, and output to the basebandsignal processing section 204. The transmitting/receiving sections 203are capable of transmitting/receiving UL/DL signals in unlicensed bands.Note that the transmitting/receiving sections 203 may be capable oftransmitting/receiving UL/DL signals in licensed bands as well.

A transmitting/receiving section 203 can be constituted by atransmitters/receiver, a transmitting/receiving circuit ortransmitting/receiving apparatus that can be described based on generalunderstanding of the technical field to which the present inventionpertains. Note that a transmitting/receiving section 203 may bestructured as a transmitting/receiving section in one entity, or may beconstituted by a transmitting section and a receiving section.

In the baseband signal processing section 204, the baseband signal thatis input is subjected to an FFT process, error correction decoding, aretransmission control receiving process, and so on. Downlink user datais forwarded to the application section 205. The application section 205performs processes related to higher layers above the physical layer andthe MAC layer, and so on. Furthermore, in the downlink data, broadcastinformation is also forwarded to the application section 205.

Meanwhile, uplink user data is input from the application section 205 tothe baseband signal processing section 204. The baseband signalprocessing section 204 performs a retransmission control transmissionprocess (for example, an HARQ transmission process), channel coding,precoding, a discrete Fourier transform (DFT) process, an IFFT processand so on, and the result is forwarded to the transmitting/receivingsection 203. Baseband signals that are output from the baseband signalprocessing section 204 are converted into a radio frequency band in thetransmitting/receiving sections 203 and transmitted. The radio frequencysignals that are subjected to frequency conversion in thetransmitting/receiving sections 203 are amplified in the amplifyingsections 202, and transmitted from the transmitting/receiving antennas201.

Note that the transmitting/receiving sections 203 receive downlinkcontrol information (DCI) including PUCCH cell configurationinformation, information as to whether or not simultaneous PUCCH andPUSCH transmission is possible, information about UCI transmissionmodes, information about UCI retention periods, etc. and/or higher layersignaling (for example, RRC signaling), from the radio base station 10,in licensed CCs and/or unlicensed CCs. In addition, thetransmitting/receiving sections 203 can transmit the PUSCH to the radiobase station 10 at least in unlicensed CCs.

FIG. 15 is a diagram to illustrate an example of a functional structureof a user terminal according to one embodiment of the present invention.

Note that, although FIG. 15 primarily illustrates functional blocks thatpertain to characteristic parts of the present embodiment, the userterminal 20 has other functional blocks that are necessary for radiocommunication as well.

The baseband signal processing section 204 provided in the user terminal20 at least has a control section 401, a transmission signal generationsection 402, a mapping section 403, a received signal processing section404 and a measurement section 405. Note that these configurations haveonly to be included in the user terminal 20, and some or all of theseconfigurations may not be included in the baseband signal processingsection 204.

The control section 401 controls the whole of the user terminal 20. Forthe control section 401, a controller, a control circuit or controlapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains can be used.

The control section 401, for example, controls the generation of signalsin the transmission signal generation section 402, the allocation ofsignals by the mapping section 403, and so on. Furthermore, the controlsection 401 controls the signal receiving processes in the receivedsignal processing section 404, the measurements of signals in themeasurement section 405, and so on.

The control section 401 acquires the downlink control signals (signalstransmitted in the PDCCH/EPDCCH) and downlink data signals (signalstransmitted in the PDSCH) transmitted from the radio base station 10,via the received signal processing section 404. The control section 401controls the generation of uplink control signals (for example, deliveryacknowledgement signals (HARQ-ACKs) and so on) and uplink data signalsbased on the downlink control signals, the results of deciding whetheror not re transmission control is necessary for the downlink datasignals, and so on.

The control section 401 may control the transmission signal generationsection 402 and the mapping section 403 to transmit uplink signals (forexample, PUCCH, PUSCH, etc.) in carriers (LBT carriers) where listeningis performed before uplink transmission, according to LBT resultsacquired in the measurement section 405.

The control section 401 determines whether or not PUCCH transmission ispossible in LAA SCells, based on information (PUCCH cell configurationinformation) as to whether or not at least one of the LBT carriers is acell where PUCCH is transmitted (“PUCCH cell,” “PUCCH SCell,” etc.),acquired from the received signal processing section 404, and controlsthe transmission of UCI in each LAA SCell.

The control section 401 can obtain information as to whethersimultaneous transmission of an uplink control channel (for example,PUCCH) and an uplink shared channel (for example, PUSCH) is possible,from the received signal processing section 404. Furthermore, if thecontrol section 401 determines that PUCCH transmission is possible inone of the LAA SCells based on the PUCCH cell configuration information,the control section 401 can further control the transmission of UCI ineach LAA SCell based on this information as to whether or notsimultaneous transmission is possible.

The control section 401 may obtain information related to UCItransmission modes, which specify in which carriers various UCIspertaining to non-LBT carriers and LBT carriers are transmitted, fromthe received signal processing section 404. Furthermore, when thecontrol section 401 determines that PUCCH transmission is not possiblein any of the LAA SCells, based on the PUCCH cell configurationinformation, the control section 401 can further control thetransmission of UCI in each LAA SCell based on this UCI transmissionmode-related information.

The control section 401 may exert control so that UE capabilityinformation as to whether PF 4/5 are supported in at least one of theLBT carriers is transmitted.

The control section 401 may exert control so that various UCIs areretained for a predetermined period of time (for example, for a firstretention period, a second retention period, etc.), and a plurality ofUCIs (for example, all UCIs of all LAA SCells) that are retained for LBTcarriers are transmitted simultaneously (together) in at least one LAASCell.

The control section 401 may control the codebook size to use to transmitan A/N based on the time the A/N (retransmission control information) isretained (for example, at least one of the first retention time (Y) andthe second retention time (X)). Also, the control section 401 maycontrol (determines) the codebook size based on the number of CCs, inaddition to the retention time of the A/N.

The codebook size may be a fixed size that is uniquely determined ineach TTI (also referred to as “fixed codebook size,” as illustrated inFIG. 17), or may be a size that is changed dynamically (also referred toas “dynamic codebook size,” as illustrated in FIG. 18 and FIG. 19). Thefixed codebook size may be equal to the maximum number of A/Ns that canbe transmitted in each TTI.

The transmission signal generation section 402 generates uplink signals(uplink control signals, uplink data signals, uplink reference signalsand so on) based on commands from the control section 401, and outputsthese signals to the mapping section 403. The transmission signalgeneration section 402 can be constituted by a signal generator, asignal generating circuit or signal generating apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains.

For example, the transmission signal generating section 402 generatesuplink control signals such as delivery acknowledgement signals(HARQ-ACKs), channel state information (CSI) and so on, based oncommands from the control section 401. Also, the transmission signalgeneration section 402 generates uplink data signals based on commandsfrom the control section 401. For example, when a UL grant is includedin a downlink control signal that is reported from the radio basestation 10, the control section 401 commands the transmission signalgeneration section 402 to generate an uplink data signal.

The mapping section 403 maps the uplink signals generated in thetransmission signal generation section 402 to radio resources based oncommands from the control section 401, and outputs the result to thetransmitting/receiving sections 203. The mapping section 403 can beconstituted by a mapper, a mapping circuit or mapping apparatus that canbe described based on general understanding of the technical field towhich the present invention pertains.

The received signal processing section 404 performs receiving processes(for example, demapping, demodulation, decoding and so on) of receivedsignals that are input from the transmitting/receiving sections 203.Here, the received signals include, for example, downlink signals(downlink control signals, downlink data signals, downlink referencesignals and so on) that are transmitted from the radio base station 10.The received signal processing section 404 can be constituted by asignal processor, a signal processing circuit or signal processingapparatus that can be described based on general understanding of thetechnical field to which the present invention pertains. Also, thereceived signal processing section 404 can constitute the receivingsection according to the present invention.

The received signal processing section 404 outputs the decodedinformation, acquired through the receiving processes, to the controlsection 401. The received signal processing section 404 outputs, forexample, broadcast information, system information, RRC signaling, DCIand so on, to the control section 401. Also, the received signalprocessing section 404 outputs the received signals, the signals afterthe receiving processes and so on, to the measurement section 405.

The measurement section 405 conducts measurements with respect to thereceived signals. The measurement section 405 can be constituted by ameasurer, a measurement circuit or measurement apparatus that can bedescribed based on general understanding of the technical field to whichthe present invention pertains.

The measurement section 405 executes LBT in carriers where LBT isconfigured, based on commands from the control section 401. Themeasurement section 405 may output the results of LBT (for example,judgments as to whether the channel state is free or busy) to thecontrol section 401.

Also, the measurement section 405 may measure the received power (forexample, RSRP), the received signal strength (RSSI), the receivedquality (for example, RSRQ) and the channel states and so on of thereceived signals. The measurement results may be output to the controlsection 401.

(Hardware Structure)

Note that the block diagrams that have been used to describe the aboveembodiments indicate blocks in functional units. These functional blocks(components) may be implemented in arbitrary combinations of hardwareand/or software. Also, the means for implementing each functional blockis not particularly limited. That is, each functional block may beimplemented with 1 piece of physically-integrated apparatus, or may beimplemented by connecting 2 physically-separate pieces of apparatus viaradio or wire and by using these multiple pieces of apparatus.

For example, the radio base station, user terminals and so on accordingto embodiments of the present invention may function as a computer thatexecutes the processes of the radio communication method of the presentinvention. FIG. 16 is a diagram to illustrate an example hardwarestructure of a radio base station and a user terminal according to oneembodiment of the present invention. Physically, the above-describedradio base stations 10 and user terminals 20 may be formed as a computerapparatus that includes a processor 1001, a memory 1002, a storage 1003,communication apparatus 1004, input apparatus 1005, output apparatus1006 and a bus 1007.

Note that, in the following description, the word “apparatus” may bereplaced by “circuit,” “device,” “unit” and so on. Note that thehardware structure of a radio base station 10 and a user terminal 20 maybe designed to include one or more of each apparatus illustrated in thedrawings, or may be designed not to include part of the apparatus.

For example, although only one processor 1001 is illustrated, aplurality of processors may be provided. Furthermore, processes may beimplemented with one processor, or processes may be implemented insequence, or in different manners, on one or more processors.

Each function of the radio base station 10 and the user terminal 20 isimplemented by reading predetermined software (program) on hardware suchas the processor 1001 and the memory 1002, and by controlling thecalculations in the processor 1001, the communication in thecommunication apparatus 1004, and the reading and/or writing of data inthe memory 1002 and the storage 1003.

The processor 1001 may control the whole computer by, for example,running an operating system. The processor 1001 may be configured with acentral processing unit (CPU), which includes interfaces with peripheralapparatus, control apparatus, computing apparatus, a register and so on.For example, the above-described baseband signal processing section 104(204), call processing section 105 and so on may be implemented by theprocessor 1001.

Furthermore, the processor 1001 reads programs (program codes), softwaremodules or data, from the storage 1003 and/or the communicationapparatus 1004, into the memory 1002, and executes various processesaccording to these. As for the programs, programs to allow computers toexecute at least part of the operations of the above-describedembodiments may be used. For example, the control section 401 of theuser terminals 20 may be implemented by control programs that are storedin the memory 1002 and that operate on the processor 1001, and otherfunctional blocks may be implemented likewise.

The memory 1002 is a computer-readable recording medium, and may beconstituted by, for example, at least one of a ROM (Read Only Memory),an EPROM (Erasable Programmable ROM), an EEPROM (Electrically EPROM), aRAM (Random Access Memory) and/or other appropriate storage media. Thememory 1002 may be referred to as a “register,” a “cache,” a “mainmemory” (primary storage apparatus) and so on. The memory 1002 can storeexecutable programs (program codes), software modules and/and so on forimplementing the radio communication methods according to embodiments ofthe present invention.

The storage 1003 is a computer-readable recording medium, and may beconstituted by, for example, at least one of a flexible disk, a floppy(registered trademark) disk, a magneto-optical disk (for example, acompact disc (CD-ROM (Compact Disc ROM) and so on), a digital versatiledisc, a Blu-ray (registered trademark) disk), a removable disk, a harddisk drive, a smart card, a flash memory device (for example, a card, astick, a key drive, etc.), a magnetic stripe, a database, a server,and/or other appropriate storage media. The storage 1003 may be referredto as “secondary storage apparatus.”

The communication apparatus 1004 is hardware (transmitting/receivingdevice) for allowing inter-computer communication by using wired and/orwireless networks, and may be referred to as, for example, a “networkdevice,” a “network controller,” a “network card,” a “communicationmodule” and so on. For example, the above-describedtransmitting/receiving antennas 101 (201), amplifying sections 102(202), transmitting/receiving sections 103 (203), communication pathinterface 106 and so on may be implemented by the communicationapparatus 1004.

The input apparatus 1005 is an input device for receiving input from theoutside (for example, a keyboard, a mouse, etc.). The output apparatus1006 is an output device for sending output to the outside (for example,a display, a speaker, etc.). Note that the input apparatus 1005 and theoutput apparatus 1006 may be provided in an integrated structure (forexample, a touch panel).

Furthermore, these types of apparatus, including the processor 1001, thememory 1002 and others, are connected by a bus 1007 for communicatinginformation. The bus 1007 may be formed with a single bus, or may beformed with buses that vary between pieces of apparatus.

Also, the radio base station 10 and the user terminal 20 may bestructured to include hardware such as a microprocessor, a digitalsignal processor (DSP), an ASIC (Application-Specific IntegratedCircuit), a PLD (Programmable Logic Device), an FPGA (Field ProgrammableGate Array) and so on, and part or all of the functional blocks may beimplemented by the hardware. For example, the processor 1001 may beimplemented with at least one of these pieces of hardware.

(Variations)

Note that the terminology used in this specification and the terminologythat is needed to understand this specification may be replaced by otherterms that convey the same or similar meanings. For example, “channels”and/or “symbols” may be replaced by “signals (or “signaling”).” Also,“signals” may be “messages.” A reference signal may be abbreviated as an“RS,” and may be referred to as a “pilot,” depending on which standardapplies. Furthermore, a “component carrier” (CC) may be referred to as a“cell,” a “frequency carrier,” a “carrier frequency” and so on.

Furthermore, a radio frame may be comprised of one or more periods(frames) in the time domain. Each of one or more periods (frames)constituting a radio frame may be referred to as a “subframe.”Furthermore, a subframe may be comprised of one or more slots in thetime domain. Furthermore, a slot may be comprised of 1 or multiplesymbols (OFDM symbols, SC-FDMA symbols, etc.) in the time domain.

A radio frame, a subframe, a slot and a symbol all represent the timeunit in signal communication. A radio frames, a subframe, a slot and asymbol may be each called by other applicable names. For example, onesubframe may be referred to as a “transmission time interval” (TTI), ora plurality of consecutive subframes may be referred to as a “TTI,” orone slot may be referred to as a “TTI.” That is, a subframe and a TTImay be a subframe (1 ms) in existing LTE, may be a shorter period than 1ms (for example, one to thirteen symbols), or may be a longer period oftime than 1 ms.

Here, a TTI refers to the minimum time unit of scheduling in radiocommunication, for example. For example, in LTE systems, a radio basestation schedules the allocation of radio resources (such as thefrequency bandwidth and transmission power that can be used by each userterminal) for each user terminal in TTI units. Note that the definitionof TTIs is not limited to this. The TTI may be the transmission timeunit of channel-encoded data packets (transport blocks), or may be theunit of processing in scheduling, link adaptation and so on.

A TTI having a time duration of 1 ms may be referred to as a “normalTTI” (TTI in LTE Rel. 8 to 12), a “long TTI,” a “normal subframe,” a“long subframe,” and so on. A TTI that is shorter than a normal TTI maybe referred to as a “shortened TTI,” a “short TTI,” a “shortenedsubframe,” a “short subframe,” and so on.

A resource block (RB) is the unit of resource allocation in the timedomain and the frequency domain, and may include one or a plurality ofconsecutive subcarriers in the frequency domain. Also, an RB may includeone or more symbols in the time domain, and may be one slot, onesubframe or one TTI in length. One TTI and one subframe each may becomprised of one or more resource blocks. Note that an RB may bereferred to as a “physical resource block” (PRB: Physical RB), a “PRBpair,” an “RB pair,” and so on.

Furthermore, a resource block may be comprised of one or more resourceelements (REs). For example, one RE may be a radio resource field of onesubcarrier and one symbol.

Note that the above-described structures of radio frames, subframes,slots, symbols and so on are merely examples. For example,configurations such as the number of subframes included in a radioframe, the number of slots included in a subframe, the number of symbolsand RBs included in a slot, the number of subcarriers included in an RB,the number of symbols in a TTI, the symbol duration and cyclic prefix(CP) length can be variously changed.

Also, the information and parameters described in this specification maybe represented in absolute values or in relative values with respect topredetermined values, or may be represented in other informationformats. For example, radio resources may be specified by predeterminedindices.

The information, signals and/or others described in this specificationmay be represented by using a variety of different technologies. Forexample, data, instructions, commands, information, signals, bits,symbols and chips, all of which may be referenced throughout theherein-contained description, may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orphotons, or any combination of these.

Also, information, signals and so on can be output from higher layers tolower layers and/or from lower layers to higher layers. Information,signals and so on may be input and output via a plurality of networknodes.

The information, signals and so on that are input may be transmitted toother pieces of apparatus. The information, signals and so on to beinput and/or output can be overwritten, updated or appended. Theinformation, signals and so on that are output may be deleted. Theinformation, signals and so on that are input may be transmitted toother pieces of apparatus.

Reporting of information is by no means limited to theexamples/embodiments described in this specification, and other methodsmay be used as well. For example, reporting of information may beimplemented by using physical layer signaling (for example, DCI(Downlink Control Information) and UCI (Uplink Control Information)),higher layer signaling (for example, RRC (Radio Resource Control)signaling, broadcast information (the MIB (Master Information Blocks)and SIBs (System Information Blocks) and so on) and MAC (Medium AccessControl) signaling, other signals or combinations of these.

Also, RRC signaling may be referred to as “RRC messages,” and can be,for example, an RRC connection setup message, RRC connectionreconfiguration message, and so on. Also, MAC signaling may be reportedusing, for example, MAC control elements (MAC CEs (Control Elements)).

Also, predetermined information (for example, reporting of informationto the effect that “X holds”) does not necessarily have to be reportedexplicitly, and can be reported in an implicit manner (by, for example,not reporting this piece of information).

Decisions may be made in values represented by one bit (0 or 1), may bemade in Boolean values that represent true or false, or may be made bycomparing numerical values (for example, comparison against apredetermined value).

Software, whether referred to as “software,” “firmware,” “middleware,”“microcode” or “hardware description language,” or called by othernames, should be interpreted broadly, to mean instructions, instructionsets, code, code segments, program codes, programs, subprograms,software modules, applications, software applications, softwarepackages, routines, subroutines, objects, executable files, executionthreads, procedures, functions and so on.

Also, software, commands, information and so on may be transmitted andreceived via communication media. For example, when software istransmitted from a website, a server or other remote sources by usingwired technologies (coaxial cables, optical fiber cables, twisted-paircables, digital subscriber lines (DSL) and so on) and/or wirelesstechnologies (infrared radiation and microwaves), these wiredtechnologies and/or wireless technologies are also included in thedefinition of communication media.

The terms “system” and “network” as used herein are usedinterchangeably.

As used herein, the terms “base station (BS),” “radio base station,”“eNB,” “cell,” “sector,” “cell group,” “carrier,” and “componentcarrier” may be used interchangeably. A base station may be referred toas a “fixed station,” “NodeB,” “eNodeB (eNB),” “access point,”“transmission point,” “receiving point,” “femto cell,” “small cell” andso on.

A base station can accommodate one or more (for example, three) cells(also referred to as “sectors”). When a base station accommodates aplurality of cells, the entire coverage area of the base station can bepartitioned into multiple smaller areas, and each smaller area canprovide communication services through base station subsystems (forexample, indoor small base stations (RRHs: Remote Radio Heads)). Theterm “cell” or “sector” refers to part or all of the coverage area of abase station and/or a base station subsystem that provides communicationservices within this coverage.

As used herein, the terms “mobile station (MS)” “user terminal,” “userequipment (UE)” and “terminal” may be used interchangeably. A basestation may be referred to as a “fixed station,” “NodeB,” “eNodeB(eNB),” “access point,” “transmission point,” “receiving point,” “femtocell,” “small cell” and so on.

A mobile station may be referred to, by a person skilled in the art, asa “subscriber station,” “mobile unit,” “subscriber unit,” “wirelessunit,” “remote unit,” “mobile device,” “wireless device,” “wirelesscommunication device,” “remote device,” “mobile subscriber station,”“access terminal,” “mobile terminal,” “wireless terminal,” “remoteterminal,” “handset,” “user agent,” “mobile client,” “client” or someother suitable terms.

Furthermore, the radio base stations in this specification may beinterpreted as user terminals. For example, each aspect/embodiment ofthe present invention may be applied to a configuration in whichcommunication between a radio base station and a user terminal isreplaced with communication among a plurality of user terminals (D2D:Device-to-Device). In this case, user terminals 20 may have thefunctions of the radio base stations 10 described above. In addition,wording such as “uplink” and “downlink” may be interpreted as “side.”For example, an uplink channel may be interpreted as a side channel.

Likewise, the user terminals in this specification may be interpreted asradio base stations. In this case, the radio base stations 10 may havethe functions of the user terminals 20 described above.

Certain actions which have been described in this specification to beperformed by base station may, in some cases, be performed by uppernodes.

In a network comprised of one or more network nodes with base stations,it is clear that various operations that are performed to communicatewith terminals can be performed by base stations, one or more networknodes (for example, MMEs (Mobility Management Entities), S-GW(Serving-Gateways), and so on may be possible, but these are notlimiting) other than base stations, or combinations of these.

The examples/embodiments illustrated in this specification may be usedindividually or in combinations, which may be switched depending on themode of implementation. The order of processes, sequences, flowchartsand so on that have been used to describe the examples/embodimentsherein may be re-ordered as long as inconsistencies do not arise. Forexample, although various methods have been illustrated in thisspecification with various components of steps in exemplary orders, thespecific orders that are illustrated herein are by no means limiting.

The examples/embodiments illustrated in this specification may beapplied to LTE (Long Term Evolution), LTE-A (LTE-Advanced), LTE-B(LTE-Beyond), SUPER 3G, IMT-Advanced, 4G (4th generation mobilecommunication system), 5G (5th generation mobile communication system),FRA (Future Radio Access), New-RAT (Radio Access Technology), GSM(registered trademark) (Global System for Mobile communications), CDMA2000, UMB (Ultra Mobile Broadband), IEEE 802.11 (Wi-Fi (registeredtrademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.20,UWB (Ultra-WideBand), Bluetooth (registered trademark), systems that useother adequate radio communication methods and/or next-generationsystems that are enhanced based on these.

The phrase “based on” as used in this specification does not mean “basedonly on,” unless otherwise specified. In other words, the phrase “basedon” means both “based only on” and “based at least on.”

Reference to elements with designations such as “first,” “second” and soon as used herein does not generally limit the number/quantity or orderof these elements. These designations are used only for convenience, asa method for distinguishing between two or more elements. Thus,reference to the first and second elements does not imply that only twoelements may be employed, or that the first element must precede thesecond element in some way.

As used herein the terms “determining” and “determining” encompass awide variety of actions. For example, to “decide” and “determine” asused herein may be interpreted to mean making decisions anddeterminations related to calculating, computing, processing, deriving,investigating, looking up (for example, searching a table, a database orsome other data structure), ascertaining and so on. Furthermore, to“decide” and “determine” as used herein may be interpreted to meanmaking decisions and determinations related to receiving (for example,receiving information), transmitting (for example, transmittinginformation), inputting, outputting, accessing (for example, accessingdata in a memory) and so on. In addition, to “decide” and “determine” asused herein may be interpreted to mean making decisions anddeterminations related to resolving, selecting, choosing, establishing,comparing and so on.

Now, although the present invention has been described in detail above,it should be obvious to a person skilled in the art that the presentinvention is by no means limited to the embodiments described herein.The present invention can be implemented with various corrections and invarious modifications, without departing from the spirit and scope ofthe present invention defined by the recitations of claims.Consequently, the description herein is provided only for the purpose ofexplaining examples, and should by no means be construed to limit thepresent invention in any way.

The disclosures of Japanese Patent Application No. 2016-073412, filed onMar. 31, 2016, and Japanese Patent Application No. 2016-101884, filed onMay 20, 2016, including the specifications, drawings and abstracts, areincorporated herein by reference in their entirety.

1. A user terminal comprising: a transmission section that transmitssignals in carriers where listening is performed before uplinktransmission; a receiving section that receives PUCCH cell configurationinformation as to whether or not at least one of the carriers is a cellwhere a PUCCH (Physical Uplink Control Channel (PUCCH) is transmitted;and a control section that controls transmission of uplink controlinformation (UCI) in the carriers based on the PUCCH cell configurationinformation.
 2. The user terminal according to claim 1, wherein: thetransmission section transmits terminal capability information as towhether or not PUCCH formats 4 and/or 5 are supported in at least one ofthe carriers; and the terminal capability information is used to controlwhether or not at least one of the carriers is the cell where the PUCCHis transmitted.
 3. The user terminal according to claim 1, wherein thereceiving section receives information as to whether or not simultaneoustransmission of the PUCCH and a Physical Uplink Shared Channel (PUSCH)is possible, and the control section, when determining that at least oneof the carriers is the cell where the PUCCH is transmitted, controls thetransmission of the UCI in the carriers based on the information as towhether or not the simultaneous transmission is possible.
 4. The userterminal according to claim 3, wherein the control section controls theUCI to be retained for a predetermined period, and the transmissionsection simultaneously transmits a plurality of UCIs pertaining to thecarriers and retained, in at least one of the carriers.
 5. The userterminal according to claim 1, wherein the receiving section receivesinformation about UCI transmission modes for specifying whether UCI ofeach carrier is transmitted in a carrier where listening is not carriedout before uplink transmission, or in a carrier where listening isperformed before uplink transmission, and the control section, whendetermining that none of the carriers is the cell where the PUCCH istransmitted, controls the transmission of UCI in the carriers based onthe information about UCI transmission modes.
 6. The user terminalaccording to claim 5, wherein the control section exerts control so thatthe UCI is retained for a first retention period before downlink controlinformation for transmitting the UCI in the Physical Uplink SharedChannel (PUSCH) is received, and retained for a second retention periodafter the downlink control information is received, and the transmissionsection simultaneously transmits a plurality of UCIs pertaining to thecarriers and retained, in at least one of the carriers, in the PUSCH. 7.(canceled)
 8. A radio communication method comprising the steps of:transmitting signals in carriers where listening is performed beforeuplink transmission; receiving PUCCH cell configuration information asto whether or not at least one of the carriers is a cell where aPhysical Uplink Control Channel (PUCCH) is transmitted; and controllingtransmission of uplink control information (UCI) in the carriers basedon the PUCCH cell configuration information.
 9. A user terminalcomprising: a receiving section that receives downlink signals; atransmission section that transmits retransmission control informationin response to the downlink signals in carries where listening isperformed before transmission; and a control section that determines acodebook size to use to transmit the retransmission control informationbased on a retention period for the retransmission control information.